System and methods for implementing regional air transit network using hybrid-electric aircraft

ABSTRACT

Systems, apparatuses, and methods for overcoming the disadvantages of current air transportation systems that might be used for regional travel by providing a more cost effective and convenient regional air transport system. In some embodiments, the inventive air transport system, operational methods, and associated aircraft include a highly efficient plug-in series hybrid-electric powertrain (specifically optimized for aircraft operating in regional ranges), a forward compatible, range-optimized aircraft design, enabling an earlier impact of electric-based air travel services as the overall transportation system and associated technologies are developed, and platforms for the semi-automated optimization and control of the powertrain, and for the semi-automated optimization of determining the flight path for a regional distance hybrid-electric aircraft flight.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/043,990, entitled “System and Methods for Implementing Regional AirTransit Network Using Hybrid-Electric Aircraft,” filed Aug. 29, 2014,which is incorporated herein by reference in its entirety (includingAppendix) for all purposes.

BACKGROUND

Transportation devices and transportation systems are an important partof the infrastructure used to enable commerce and the movement of peoplebetween locations. As such, they are essential services for the growthof an economy, the development of a society, and the effectivegovernance of a region. Transportation devices and systems are used tomove goods between distributions points, enable face-to-face meetingsand discussions, and in general to facilitate the growth ofrelationships. Further, as new modes of transportation have developed,travel times and cargo carrying abilities have changed drastically,enabling new and often faster methods of communications and the deliveryof goods and services. In this regard, over the years, several primarytypes of transportation systems have been developed; however, eachtypically has its own focus, advantages, and drawbacks compared to othermodes of transportation.

For example, in the United States today, over 100 years after the firstpowered flight, the vast majority (>97%) of regional long-distance trips(i.e., 50 to 500 miles) are made by personal auto. Although countrieswith extensive rail systems may divert 10-15% of trips to rail, thisstill leaves well over 80% of trips to be made by auto. This isinefficient and may also not be in the best interests of society atlarge, as it translates to poor mobility (relatively long door-doortimes), creates pollution, and puts stress on the existing highwayinfrastructure. However, current commercial air services over this rangeare often relatively costly and inconvenient. One reason for thisinefficiency is that the shorter flight distances mean that a relativelylarge fraction of the total travel time (>70%) is spent on the ground(where this “ground” time includes traveling to and from airports,traversing terminals, at the gate or taxiing on the tarmac). As aresult, in such situations, air transportation is generally not adesirable mode of transport and is currently used for less than 1% ofsuch regional trips.

Aviation transport services for people and cargo have doubledapproximately every 15 years, enabling unprecedented global mobility andcargo distribution. In contrast, the relatively poor value proposition(and hence usage) of air travel over regional ranges might be considereda striking failure; even more so, given that almost all (94%)long-distance travel is regional. In this sense there is a demonstratedneed for a desirable form of regional distance air transportation, but alack of a desirable system for satisfying that need.

This failure to develop an effective and efficient form of regional airtransportation has led to stagnant door-to-door travel times and hasbeen a significant factor in limiting mobility improvements in theUnited States for several decades. This is highly undesirable, aslimited mobility impacts business and pleasure travel, job developmentand opportunities, educational choices, and other factors which arebeneficial to the growth and prosperity of society. In some regards, theviability of regional air transportation has actually declined steadilysince the 1960s as airlines have shifted to larger aircraft and longerranges in order to respond to competitive pressures and to lower thecost-per-passenger-mile of transportation. Thus, the present economicforces are causing current methods of providing air transportation tomove steadily away from the types of systems and methods describedherein.

As will be described, conventional approaches to providing air transportservices for regional travel are not sufficiently convenient oreffective for purposes of encouraging widespread use by potentialcustomers. Embodiments of the invention are directed toward solvingthese and other problems individually and collectively.

SUMMARY

The terms “invention,” “the invention,” “this invention” and “thepresent invention” as used herein are intended to refer broadly to allof the subject matter described in this document and to the claims.Statements containing these terms should be understood not to limit thesubject matter described herein or to limit the meaning or scope of theclaims. Embodiments of the invention covered by this patent are definedby the claims and not by this summary. This summary is a high-leveloverview of various aspects of the invention and introduces some of theconcepts that are further described in the Detailed Description sectionbelow. This summary is not intended to identify key, required, oressential features of the claimed subject matter, nor is it intended tobe used in isolation to determine the scope of the claimed subjectmatter. The subject matter should be understood by reference toappropriate portions of the entire specification of this patent, to anyor all drawings, and to each claim.

As recognized by the inventors, the failure of modern aviation servicesto address the need for regional air transport is a direct outcome ofthe use of conventional aircraft technology. It is well known by thoseexperienced in the art that optimizing conventional aircraft forregional operations results in design and performance compromises whichadversely affect efficiency. For example, gas turbines (jet andturboprop engines) suffer a significant decrease in efficiency at loweraltitudes and slower speeds, and a further loss of efficiency whenscaled to smaller sizes. In addition, short runway operations impose apenalty in wing and/or engine sizing larger than optimal for efficientcruise performance. As a result, large aircraft over long-ranges offerthe lowest operating costs per passenger-mile, with rapidly increasingcosts for distances <500 miles, and for aircraft seating fewer than 100passengers (or an equivalent cargo weight of 25,000 lbs). Note thatgiven a relatively poor efficiency on the ground or in climbing mode,scaled down gas turbines cost more to operate at short-ranges relativeto longer ranges (where for shorter ranges, ground or climbing time mayrepresent a significant and relatively larger percentage of the overalltravel time).

This inefficient cost relationship shapes many of the aspects ofaviation services today. Competitive pressures have driven airlines tomigrate to larger aircraft and longer flights. This has led to fewerflights from a smaller number of hub airports that can generatepassenger volumes sufficient to support the larger aircraft. Forexample, the United States has approximately 13,500 airports; yet, 70%of the air traffic is concentrated in 29 hubs and 96% is concentrated in138 hubs. Fewer flights from a small number of increasingly congestedhubs, coupled with long ground transit times have in turn caused therelatively low utility of air transportation for purposes of regionaltravel. Further, the recent, heavier focus on “capacity discipline” bythe airlines has exacerbated the problem as airlines seek to concentratedemand to even fewer hubs.

Embodiments of the invention are directed to systems, apparatuses, andmethods for overcoming the disadvantages of current air transportationsystems that might be used for regional travel by providing a more costeffective and convenient regional air transport system. In someembodiments, the inventive air transport system, operational methods,and associated aircraft include one or more of the following elements,functionality, or features:

-   1. A highly efficient plug-in series hybrid-electric powertrain,    specifically optimized for aircraft operating in regional ranges;-   2. A forward compatible, range-optimized aircraft design, enabling    an earlier impact of electric-based air travel services as the    overall transportation system and associated technologies are    developed; and-   3. Platforms for the semi-automated optimization and control of the    powertrain, and for the semi-automated optimization of determining    the flight path for a regional distance hybrid-electric aircraft    flight.

In one embodiment, the invention is directed to a hybrid-electricaircraft, wherein the aircraft includes:

-   -   a source of energy, the source of energy including a source of        stored electrical energy and a source of generated energy        provided by a generator;    -   a powertrain, the powertrain operable to receive as an input        energy from the source of energy and in response to operate one        or more electrically powered motors;    -   one or more propulsors, wherein each propulsor is coupled to at        least one of the one or more electrically powered motors;    -   an electronic processor programmed with a first set of        instructions, which when executed provide one or more functions        or processes for managing the operation of the aircraft, wherein        these functions or processes include a function or process for        -   determining a status of the amount of stored electrical            energy and generator fuel presently available to the            aircraft;        -   determining an amount of stored electrical energy and            generator fuel required to enable the aircraft to reach its            intended destination;        -   determining an amount of energy that could be generated by            the source of generated energy presently available to the            aircraft;        -   determining how to optimally draw energy from the sources of            stored electrical energy and generated energy; and        -   in event of failure or abnormal operation of a component of            the powertrain, determining a reconfiguration of the            powertrain and a revised control strategy for continued            flight;    -   an electronic processor programmed with a second set of        instructions, which when executed provide one or more functions        or processes for planning a flight for the aircraft, wherein        these functions or processes include a function or process for        -   accessing data regarding the total amount of stored            electrical energy and generator fuel presently available to            the aircraft;        -   determining if the amount of stored electrical energy and            generator fuel presently available to the aircraft is            sufficient to enable the aircraft to reach its intended            destination, wherein this includes consideration of a first            aircraft operating mode wherein stored electrical energy is            used exclusively and consideration of a second aircraft            operating mode wherein a combination of stored electrical            energy and generated energy is used;        -   if the amount of stored electrical energy and generator fuel            presently available to the aircraft is sufficient to enable            the aircraft to reach its intended destination, then            planning a route to the intended destination;        -   if the amount of stored electrical energy and generator fuel            presently available to the aircraft is sufficient to enable            the aircraft to reach its intended destination, then            planning how to optimally draw energy from the sources of            stored electrical energy and generated energy over the            planned route to the intended destination;        -   if the amount of stored electrical energy and generator fuel            presently available to the aircraft is insufficient to            enable the aircraft to reach its intended destination, then            planning a route to an intermediate destination, wherein            planning a route to an intermediate destination further            includes            -   determining one or more possible energy and/or fuel                providers;            -   determining if available stored energy and generator                fuel are sufficient to reach at least one of the                providers;            -   generating a route to the at least one provider; and            -   planning how to optimally draw energy over the route;                and    -   a communications element or elements operable to enable data        from the aircraft to be transferred to a remote data processing        platform or operator and to receive data from the remote data        processing platform or operator for exchanging data regarding        one or more of route planning or recharge and refuel sources.

In another embodiment, the invention is directed to a regional airtransportation system that includes a plurality of the inventivehybrid-electric aircraft, a plurality of aircraft take-off or landingsites, wherein each take-off or landing site includes a recharge andrefuel platform operable to provide recharging services for a source ofstored electrical energy and fuel for a source of generated energy, anda data processing system or platform, wherein the data processing systemor platform is operable to provide route planning data to one or more ofthe plurality of hybrid-electric powered aircraft.

In yet another embodiment, the invention is directed to a non-transitorycomputer readable medium on which are contained a set of instructions,wherein when executed by a programmed electronic processing element, theset of instructions cause an apparatus containing the electronicprocessing element to:

-   -   determine a status of the amount of stored electrical energy and        generator fuel presently available to a hybrid-electric powered        aircraft;    -   determine an amount of stored electrical energy and generator        fuel required to enable the hybrid-electric powered aircraft to        reach its intended destination;    -   determine an amount of energy that could be generated by a        source of generated energy presently available to the        hybrid-electric powered aircraft;    -   determine how to optimally draw energy from the sources of        stored electrical energy and generated energy; and    -   in event of failure or abnormal operation of a component in the        powertrain, determine a reconfiguration of the powertrain, and a        revised control strategy for continued flight.

Other objects and advantages of the present invention will be apparentto one of ordinary skill in the art upon review of the detaileddescription of the present invention and the included figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention in accordance with the present disclosurewill be described with reference to the drawings, in which:

FIG. 1 is a diagram illustrating certain of the primary components,elements, and processes that may be present in an implementation of anembodiment of the inventive transportation system 100;

FIG. 2 is a diagram illustrating certain of the primary components,elements, data flows, and processes that may be present in animplementation of an embodiment of the inventive transportation system200;

FIG. 3 is a diagram further illustrating certain of the primarycomponents, elements, and processes that may be present in animplementation of an embodiment of the inventive transportation system300;

FIG. 3(A) is a flowchart or flow diagram illustrating a process, method,operation, or function to determine recharge and refuel servicesrequired at a destination airport, and which may be used in animplementation of an embodiment of the inventive systems and methods;FIG. 3(B) is a flowchart or flow diagram illustrating a process, method,operation, or function to determine recharge and refuel services enroute to a destination airport, and which may be used in animplementation of an embodiment of the inventive systems and methods;

FIG. 4 is a diagram further illustrating certain of the primarycomponents, elements, and processes that may be present in animplementation of an embodiment of the inventive transportation system400;

FIG. 5 is a diagram illustrating an example of the inventiverange-optimized hybrid-electric aircraft 500 that may be used in animplementation of the inventive regional air transport system;

FIG. 6 is a diagram illustrating a variable pitch electric ducted fanintegrated propulsion system 600 that may be used in an embodiment of anelectric-hybrid aircraft that is part of the inventive airtransportation system;

FIG. 7 is a diagram illustrating a powertrain 700 and its associatedelements that may be used in an embodiment of an electric-hybridaircraft used as part of the inventive air transportation system;

FIG. 8 is a schematic of a series hybrid drive configuration 800 for arepresentative aircraft that may be used in implementing an embodimentof the inventive transportation system;

FIG. 9 is a diagram illustrating an example user interface 900 for useby a pilot of an embodiment of the inventive aircraft;

FIG. 10 is a diagram illustrating the primary functional elements ormodules of a powertrain optimization and control system (POCS) that maybe used in an embodiment of an electric-hybrid aircraft that may be usedas part of the inventive air transportation system;

FIG. 11 is a diagram illustrating the primary functional elements ormodules of a POCS that may be accessed and used to control or modifyon-aircraft processes in an embodiment of the inventive airtransportation system;

FIG. 12 shows the interface configuration for an example powertrain 1200coupled to the POCS onboard by several interfaces/connectors 1202 forpurposes of sensing a performance parameter and returning a controlsignal to a component of the powertrain or its control system;

FIG. 13 is a diagram illustrating an example flight path optimizationfor an aircraft that may be generated by the Flight Path OptimizationPlatform (FPOP) and used at least in part to control the operation ofthe aircraft in an embodiment of the inventive regional airtransportation system;

FIG. 14 is a flowchart or flow diagram illustrating certain of theinputs, functions, and outputs of a Flight Path Optimization Platform(the FPOP) that may be used to determine or revise a flight path for anelectric-hybrid aircraft that may be used as part of the inventive airtransportation system;

FIG. 15 is a flow chart or flow diagram illustrating a hybrid-electricaircraft design process that may be used in implementing an embodimentof the inventive air transportation system;

FIG. 16 is a diagram of an example of a hybrid-electric aircraftdesigned in accordance with the principles and processes describedherein;

FIG. 17 is a diagram illustrating the efficiency of a certain aircraftand propulsor configuration as a function of flight altitude andrequired power;

FIG. 18 is a diagram illustrating several regional zones and theassociated airports or landing areas that may be used as part ofimplementing an embodiment of the inventive regional air transportationsystem; and

FIG. 19 is a diagram illustrating elements or components that may bepresent in a computer device or system 1900 configured to implement amethod, process, function, or operation in accordance with an embodimentof the invention.

Note that the same numbers are used throughout the disclosure andfigures to reference like components and features.

DETAILED DESCRIPTION

The subject matter of embodiments of the present invention is describedhere with specificity to meet statutory requirements, but thisdescription is not necessarily intended to limit the scope of theclaims. The claimed subject matter may be embodied in other ways, mayinclude different elements or steps, and may be used in conjunction withother existing or future technologies. This description should not beinterpreted as implying any particular order or arrangement among orbetween various steps or elements except when the order of individualsteps or arrangement of elements is explicitly described.

Embodiments of the invention will be described more fully hereinafterwith reference to the accompanying drawings, which form a part hereof,and which show, by way of illustration, exemplary embodiments by whichthe invention may be practiced. This invention may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will satisfy the statutory requirements and conveythe scope of the invention to those skilled in the art.

Among other things, the present invention may be embodied in whole or inpart as a system, as one or more methods, as one or more elements of anaircraft or transportation system, as one or more elements or functionalmodules of an aircraft (flight) control system or regional aircrafttransportation system control system, or as one or more devices.Embodiments of the invention may take the form of a hardware implementedembodiment, a software implemented embodiment, or an embodimentcombining software and hardware aspects. For example, in someembodiments, one or more of the operations, functions, processes, ormethods described herein for use in the flight control (or other form ofcontrol) of an aircraft or of a transportation system may be implementedby one or more suitable processing elements (such as a processor,microprocessor, CPU, controller, etc.) that is part of a client device,server, or other form of computing or data processing device/platformand that is programmed with a set of executable instructions (e.g.,software instructions), where the instructions may be stored in asuitable data storage element. In some embodiments, one or more of theoperations, functions, processes, or methods described herein may beimplemented by a specialized form of hardware, such as a programmablegate array, application specific integrated circuit (ASIC), or the like.The following detailed description is, therefore, not to be taken in alimiting sense.

Prior to describing multiple embodiments of the inventive aircraft andassociated regional air transport network, it is noted that thefollowing acronyms or terms may be used herein, and are meant to have atleast the indicated meaning with regards to concepts, processes, orelements:

-   -   ADS-B: Automatic Dependent Surveillance-Broadcast—the air-to-air        and air-to-ground communication and data which allow NextGen air        traffic control.    -   ATC: Air Traffic Control—refers to both the controller, and the        flight path assigned to the aircraft.    -   BPF: Blade Passage Frequency, in Hz for a ducted fan. Calculated        as rotational frequency (Hz) divided by number of blades.    -   Conventional aircraft engine: combustion engines currently in        use to provide aircraft propulsion, including, but not limited        to, reciprocating or rotary internal combustion engines, gas        turbines, turboprops, turbojets, turbofans, and ram jets.    -   COT: Cost Of Time—in this context refers to the cost of time for        the passengers or payload. For example, a business jet assigns a        very high cost of time for their passengers, while cargo has a        much lower COT. A measure of the “value” (and hence a factor in        the pricing) of an amount of time to a particular passenger, for        a piece of cargo, etc.    -   DOC: Direct Operating Cost, calculated as the sum of energy        (fuel, and/or electricity), energy storage unit amortization,        and maintenance reserves for airframe and range extending        generators or engines.    -   Ducted Fan: A multi-bladed aerodynamic propulsor located in an        axial flow duct. The duct is shaped to maximize the efficiency        of the fan.    -   FMS: Flight Management System, an integrated computer system        which controls an aircraft through an auto-pilot and        auto-throttle interface. The FMS is typically programmed prior        to take off and can fly the aircraft without pilot intervention        much, or all, of the way to the destination.    -   I: Indirect costs of operation on an hourly basis, including        airframe depreciation, crew costs, insurance, etc.    -   Mach number: The fraction of the speed of sound that a vehicle        is moving.    -   Range extending generator: May be comprised of internal        combustion engines, each driving one or more motor-generators;        alternately, could be comprised of units that convert stored        chemical energy directly to electricity, e.g., hydrogen fuel        cells.    -   Rechargeable Energy Storage Unit: comprised of battery packs,        supercapacitors, or other media for storing electrical energy        (or a combination thereof), coupled with a battery management        system(s) that manages operation and safety of the packs. Each        pack may comprise of multiple individually removable battery        modules, and operate either with some or all of these modules in        place. Also referred to as an “Energy storage unit”.    -   Solidity: measure of area of the propeller disk occupied by        blades. Defined as the ratio of total blade chord at a given        radius to the circumference of the fan disk at that radius.    -   STOL: Short Take Off and Landing—not a rigid definition, but        implies significantly shorter runway lengths, and steeper        approach angles than a similarly sized, non-STOL equipped        aircraft.    -   TDI: Turbo Diesel Injection—a compression ignition engine with        boosted intake manifold pressure.

In some embodiments, the inventive transportation network may be definedby airports (and associated ground transport options), aircraft, anddemand-supply mechanisms optimized for regional electric air transportservices. This combination of technologies, processes, devices, andcontrol methods may be used to provide multiple benefits to users.Regional electric air transport offers significantly lower door-doortravel times and cost per mile than alternate travel modes: highways,high-speed rail, and conventional air. As a result, the inventive systemwill drive and support four large-scale applications:

A. Scheduled commercial: Regional electric air will be capable ofoffering twice the door-to-door speed of conventional air atapproximately half the fare, along with convenience and comfort. Unlikethe highly concentrated air network of today, large aircraft flying longranges to a declining set of high-volume hubs, the inventive regionalelectric air network will be (much) more distributed. Smaller aircraftflying lower will serve a large number of community airports. Thegreater choice of schedules and destinations, along with low-trafficroutes will result in a far more personalized travel experience thanobtained from air travel today. Regional electric air will serve twomajor pools of demand: point-to-point and feeder. Point-to-point flightswill serve destination pairs within a region, typically bypassingconventional aircraft and hub airports. Feeder flights will transportpassengers from their local regional airports to more distantconventional hubs to connect to a long-haul flight out of the region.Conversely, feeders will transport passengers arriving on long-haulflights to their local regional airport. Both will dramatically reducedoor-to-door travel times for regional as well as long-haul travel, bybypassing congested hubs and by reducing ground legs;

B. Business and on-demand: The value proposition of a regional electricair transportation system for business and on-demand travel is also astrong one. Electric aircraft offer comfortable travel over regionalranges at 80 to 90 percent lower costs than business jets. In addition,quiet STOL (short takeoff and landing) capabilities will open upall-hours access to a large pool of smaller airports, offeringdoor-to-door times comparable to faster business jets, which requirelonger runways and create noise pollution and other problems. Moreover,the disruptively low costs of electric air transportation will expanddemand for this form of travel, while sharing technologies will multiplyusage options. In addition to air taxi, charter, and fractionalownership modes available today, capacity may also be offered on ashared or on-demand basis. For example, on shared flights, open seats onexisting flights will be offered to other passengers often at reducedfares. On-demand flights, on the other hand, will be scheduled based onpassenger volumes. These will include an on-demand marketplace that willaccept passenger requests for flights, enabling flights to be scheduledbased on a combination of requests and historical demand patterns;

C. Cargo: Even as the regional transport infrastructure has stagnatedover the past decades, the demand for fast delivery of goods hasmultiplied, driven by the rapid growth of online commerce. Electric airtransportation will offer a disruptive alternative, offering door-doorspeeds 4 to 5 times faster than ground, at comparable or lower cost.This will be enabled via cargo flights (manned, remotely piloted orautonomous) from airports at or near regional logistics hubs to airportsat or near local depots. As example, fast delivery of goods to a home orbusiness will be enabled by electric air transport cargo flights betweenregional distribution centers and local supply depots. Electric aircraftwill be loaded at the distribution centers with packages routed to oneor multiple local supply depots. Once loaded, aircraft will take-offfrom adjacent or nearby airstrips for regional flights to airstripsadjacent to or near each of the local supply depots to which cargo isaddressed. Delivery from the local depot to the final destination mayuse an existing mode, e.g., delivery truck, or one of several emergingplatforms, e.g., autonomous vehicle, delivery drone. As another example,fast delivery of goods to point of use will be enabled by electric airtransport flights from the corresponding point of production (e.g.,manufacturing facility, farm) or logistical hub (e.g., warehouse,transport terminal). Electric aircraft will be loaded at the point ofproduction or logistical hub, take off from nearby airstrips for fastflights to airstrips near the point of use;

D. Military: Despite tremendous advances in military technology over thepast decades, development of platforms to transport troops or cargo overregional distances has largely stagnated, and remain limited largely toground convoys, or the much less cost effective conventional aircraft orrotorcraft. In much the same way as for cargo, electric aircraft couldtransform regional military logistics, by enabling the shift of afraction of supply convoys from ground to electric aircraft. Doing sowould reduce exposure to enemy action, increase supply chain velocity bya significant factor (estimated to be a factor of 5 or greater), atcosts comparable to or below that of ground transport. As an example,fast supply of forward bases could be enabled by electric air transportflights from theatre logistical hubs. Electric aircraft could be loadedat a logistical hub with troops and cargo routed to one or multipleforward bases. Once loaded, aircraft will take off from a nearbyairstrip for regional flights to airstrips near each of the forwardbases addressed. Delivery could also be made without touchdown at theforward bases, using parachutes or other mechanisms to direct the cargoto the base safely. Other opportunities include replacing conventionalaircraft or rotorcraft on tactical transport missions for faster travel,increased stealth, and significantly lower cost; and

E. Manned and un-manned: Given the rapid and continued development ofautonomous vehicles and remotely piloted drones, the four applicationsof regional electric air transport services described above may includeconventionally piloted aircraft, as well as aircraft that are designedwith increasing degrees of autonomy. These will include piloted aircraftequipped for back-up control by a remote pilot, unmanned aircraftcontrolled by a remote pilot, and semi-autonomous aircraft equipped forback-up control by a remote pilot.

In one embodiment, the inventive regional air transport network mayinclude 4-classes of airports, most with runways >1,500 ft (or pads forVTOL aircraft), and differentiated based on their respective role in theregional network and the degree to which they are equipped to supporthigh-frequency hybrid-electric flights:

-   -   Regional tier I, II and III airports. These are the primary        nodes of the regional network. Tier I airports are best equipped        for high-frequency electric flights, and offer fast recharge and        swap stations, and capabilities for all-weather and night        operations. Some of the tier I airports may also be served by        scheduled flights of conventional aircraft. Tier II airports        include fast recharge and swap station, while Tier III have        basic recharge capabilities on the tarmac. Unlike conventional        hubs, regional airports will offer fewer or a lesser degree of        ground services, e.g., baggage, security, given the relatively        lower traffic volumes and smaller aircraft. This will enable        quick transit through the airport, further reducing door-to-door        travel times;    -   Mainline large hubs in-region. A subset of the large commercial        hubs located in-region, with support for flights of small to        medium hybrid electric aircraft. These could include dedicated        short runways, non-interfering flight corridors, relatively fast        recharge and swap stations, quick passenger transfer from        regional electric to conventional air flights and vice versa.        Given that a significant fraction of the regional electric        flights will be “non-sterile”, the hubs could also include        provisions for this traffic to access sterile areas of the        airport, e.g., baggage and security services to “sterilize”        arriving regional passengers;    -   Regional service hubs. Airports in region equipped to service        and house the electric aircraft. These are typically a subset of        the regional tier I or II airports, and typically will include        parking, maintenance facilities, and operations centers; and    -   Cargo airports. Airports that enable regional transport of goods        between network hubs or distribution centers and local delivery        depots. These are equipped for high-frequency electric flights        just like the tier I, II and III airports described above, and        could include shared cargo and passenger facilities. These cargo        airports are typically located near points of origin of the        goods, e.g., network hubs, distribution centers, or points of        delivery of the goods, e.g., local delivery depots.

In some embodiments, the inventive hybrid-electric range optimizedaircraft and associated regional air transport network may provide arelatively more quiet, cost-effective, energy efficient, and moreconvenient mode of transportation while also providing multiple relatedsocial and economic benefits. Such benefits include a reduction in theneed to rely on automobiles for regional transportation, which would beexpected to provide a reduction in pollution and traffic congestion. Theinventive aircraft and system also may save passenger time, lead to anincrease in productivity, encourage greater local development andhousing, support decentralized living and working arrangements, andcreate new markets for connecting transportation services.

To permit realization of the opportunities presented by a more effectiveand efficient regional air transportation system, the inventors haverecognized a need for several enabling devices, systems, data processingmethods, and technologies. These include, but are not limited to ahighly efficient and quiet short-take off capable hybrid-electricaircraft, and the associated and properly optimized technologies forregional operations “close-in” to communities and urban centers. Inaddition, there is a need for a regional transit network comprised ofsuch aircraft, supporting airports, and the appropriate demand-supplymatching mechanisms. Elements of embodiments of the invention aredesigned to address these and other needs. In particular, embodiments ofthe inventive system and methods may include one or more of:

-   -   Highly efficient plug-in series hybrid-electric powertrain        optimized for regional ranges. The powertrain may be designed to        minimize the energy required by sizing the powertrain for fast        cruise over a prescribed fraction of the range that represents a        majority of the flights, slower for longer ranges. This allows a        downsized generator, with power output less than required for        standard cruise, so that the energy storage units are used        continuously and fully depleted (less FAA required reserve)        during a flight. This also enables a relatively high energy        storage mass fraction in the range 12-20% of the total weight of        the aircraft. This higher ratio of electric storage to generated        power relative to conventional hybrid designs (and often with        generation optimized for cruise mode) is one key to the 65-80%        lower DOC (than conventional aircraft) delivered by the        inventive designs. Further reductions are enabled by        regenerative braking of the propulsors and all electric ground        operations;    -   Range optimized aircraft design enabling early impact of        electric air. Efforts to design commercial electric aircraft        to-date have focused on size, speed, and range capabilities        comparable to that of conventional aircraft. Given the range        times speed squared scaling of energy required for a flight,        this leads to designs that are either “mildly electric”, and        store only a small fraction of the energy onboard, or that are        more electric but require advanced electric technologies. This        has led to the view that electric air delivers limited savings        in the near-term, and that key technologies will take a decade        or more to mature. In contrast, by tailoring the inventive        aircraft to regional ranges, and lower speeds, altitudes, sizes,        the inventive “range optimized” designs can deliver        significantly lower DOC based on technologies that will be        available within significantly less time. This enables        market-entry many years earlier.    -   A built-in degree of “future proofing” (such as prevention of        relatively rapid technical or business related obsolescence) via        a modular, forward-compatible powertrain-propulsion coupled with        forward-compatible airframes. As with electric vehicle        technologies that are improving rapidly, a key barrier to early        adoption of electric aircraft is obsolescence driven by        technology evolution. This possible disincentive to adoption of        electric aircraft and the associated transportation system is        countered by a modular, forward-compatible design of the        powertrain, propulsion and airframe to enable technology        upgrades via simple module swaps. This enables early entry with        hybrid-electric aircraft that deliver continually improving DOC        via upgrades to stay abreast of energy storage technology and/or        improvements in operational efficiency. Another important        enabler is the inventive hybrid aircraft Powertrain Optimization        and Control System (referred to herein as “POCS”). This platform        adjusts operation of the modular powertrain based on        characteristics of the onboard energy storage units and        generator to deliver optimal performance. As a result,        technology upgrades are readily accommodated: flight objectives,        speed, efficiency, noise, payload are translated to control the        powertrain in a way that best leverages the modules onboard,        without need for extensive operator or pilot intervention;    -   Quiet operation with short-takeoff-and-landing (STOL)        capabilities to enable “close-in” flights and greater community        acceptance. Quiet STOL capabilities dramatically improve the        ability of an aircraft to fly “close in” to communities and        population centers, thereby delivering step-change reduction in        door-door travel times. STOL enables operations to smaller        community airports (>13,000 in the U.S.), bypassing congested        hubs. Quiet operation translates to greater community        acceptance, often a limiter for such flights. The inventive        system and aircraft leverage quiet electric ducted        variable-pitch fans (referred to herein as “eFans”) for        propulsion to reduce runway requirements and lower noise levels,        thereby enabling operations at a vast majority of existing        airports. The proposed inventive fan design has aerodynamics and        acoustics optimized for the intermediate speeds and altitudes of        the range-optimized aircraft. This includes use of a        low-pressure ratio variable pitch fan, enabling tailoring of        propeller blade pitch to flight mode for greater efficiency, and        use of regenerative braking to replace typically noisy spoilers.        The fan is powered by one or more high-density electric motors        located at the center of the duct and connected to the fan        directly, or through an optional elliptical reduction drive. The        high torque at low RPM of the electric motors coupled with the        high static thrust of the ducted fan leads to good STOL        performance. The combination of low fan tip speeds, fan-stator        and duct acoustic design and duct acoustic treatments deliver        significantly lower noise signatures. As an added benefit, the        increased safety and “jet like” appearance of the ducted fan are        expected to translate to strong consumer appeal relative to open        propeller aircraft often used for regional operation. The        aircraft and powertrain also include other features intended to        reduce cabin and environmental noise;    -   A distributed regional hybrid-electric air transit network for        passengers and cargo to enable effective large-scale operation        of the inventive electric aircraft. Aviation services today        require passengers (or transporters of cargo) to mold their        travel to the flight patterns of large, cost competitive        aircraft. In contrast, and as recognized by the inventors,        hybrid-electric technologies enable the opposite, to mold        aircraft and flight patterns to passenger travel needs. This is        implemented via a distributed regional electric air transport        network, operating out of a relatively large number of        neighborhood and community airports, and operating smaller        electric aircraft that are optimized to individual routes. The        form of this network will differ significantly from conventional        long-haul air transport networks and systems, leading to        distinct requirements for the constituent elements and processes        used to implement and operate the network. These are described        herein and include requirements for airports (including ground        transport options) and aircraft, to demand-supply matching        mechanisms. With regards to airports, in one embodiment this        includes 4-classes of airports all with runways >1,500 ft (or        VTOL pads) and differentiated based on role in the regional        network and degree to which they are equipped to enable        high-frequency electric flights. In terms of aircraft, in one        embodiment this includes hybrid-electric aircraft designed for        “lean” operations in-flight and on the ground at lower service        community airports. These elements are coordinated and their use        optimized using next-generation regional capacity management, to        improve aircraft load factors and utilization;    -   Development and use of a fault-tolerant design of the aircraft        powertrain for aviation-grade safety, a critical requirement for        large-scale application of hybrid-electric powertrain. In one        embodiment, this is addressed by designing the powertrain and        supporting optimization and control system (the “POCS” system)        for a relatively high-degree of redundancy to ensure continued        safe operation when faults occur. This may include features        offering redundancy in event of faults of the power sources,        converters, sensors or motors, among other elements or        processes. Other safety features may include those used to        prepare the powertrain ahead of a crash to ensure the platform        and modules respond to impact in ways to minimize risk to the        aircraft occupants;    -   Use of a powertrain designed for semi-automated optimization and        control, a factor that is critical for pilot acceptance and to        enable high-frequency operations at optimal efficiency. A key to        pilot acceptance of hybrid-electric aircraft is a control        platform with a simple pilot interface that mimics the operation        of a conventional aircraft. This platform (an example of which        is illustrated in FIG. 9, and described further herein) should        optimize the operation of powertrain modules to meet the        objectives of the pilot for the flight, across the integrated        powertrain (e.g., generator operation over course of a flight),        and for each module (e.g., motor RPM and torque for maximum        efficiency). In addition, the control platform (i.e., the POCS)        should support safe operation of the powertrain, through        appropriate fault isolation and recovery mechanisms. Other        features of the control platform may include streamlined        powertrain preparation and checks pre-flight, assisted        diagnostics and maintenance post-flight and simple calibration        following power module swaps. Many of these features or        requirements are enabled via the noted powertrain optimization        and control system (POCS) that serves as a single control        platform for the powertrain and its modules; and    -   Automated optimization methods for generating and correcting        flight paths for regional hybrid-electric flights. Note that        unlike long-haul flights by conventional jets, with well-defined        optimal altitudes and speeds, determining an optimal path for        one or more regional hybrid-electric flights (typically flying        at <30,000 ft altitude) is more complex. For example, the        differing operating characteristics of the various power sources        lead to varying optimal flight altitudes based on the degree to        which the generator is required during the flight. Thus, the        operating characteristics of the power sources need to be        considered, along with physical conditions during the flight        (e.g., terrain, weather and flight distance), and pilot        preference for the flight (e.g., high speed or economy) to        determine an optimal path. In some embodiments, this is enabled        via a Flight Path Optimization Platform (referred to herein as        “FPOP”, and described with reference to FIGS. 13 and 14) that        engages with the flight management system (FMS) and POCS to        define optimal flight paths and to refine these as conditions        evolve along the flight.

FIG. 1 is a diagram illustrating certain of the primary components,elements, and processes that may be present in an implementation of anembodiment of the inventive transportation system. As described herein,the inventive transportation system and associated apparatuses andprocesses may include a distributed air transit network for regionaltransport based on small to mid-sized (6-90 seats) hybrid and electricaircraft (having V/STOL capabilities). These are used to complement thecurrent conventional long-haul air transport systems concentrated at asmall number of hub airports.

The air transit network is tailored for high frequency operations ofelectric aircraft to a large number of regional airports currently notadequately served by conventional air, as well as low-impact operationsinto major hubs. This enables airlines, transit authorities, air-taxi,charter and cargo operators to offer profitable fixed or variableschedule and on-demand flights across the region at cost structurescompetitive with long-haul. The inventive transportation network offerssignificantly lower door-door travel times and lower total costs permile than alternate regional travel modes: highways, rail or high-speedrail, conventional air. In some embodiments this is accomplished viaconvenient, high-frequency “close-in” flights to a large number ofregional airports near communities and population centers, using theinventive quiet range-optimized hybrid-electric aircraft.

As shown in the figure, an embodiment of the inventive transportationnetwork 100 may include one or more regional sub-networks 102. Eachsub-network 102 may be affiliated with a region of a country, state, orother geographical region. Each sub-network 102 will typically includemultiple cities and one or more regional or hub airports 104 from whichoperate one or more of the inventive aircraft 106. Each regional air orhub airport 104 may include elements and services to support thescheduling and “fueling” of aircraft, where here fueling refers to therecharge or swap of the stored energy units, and adding fuel for therange-extending generators (as suggested by “Recharge and refuelservices” 108 in the figure). Management of the scheduling, refueling,and other services (such as record keeping) may be performed by one ormore service platforms 110. Such platforms may include those used toaccess and process diagnostic information regarding flights, operate afueling station, and schedule refueling operations. In some embodiments,service platforms 110 may include processes capable of performingsupply-demand matching for scheduling flights, making parts available inan efficient manner, or other desirable matching or optimizationprocesses related to management of the network and its constituentelements.

FIG. 2 is a diagram illustrating certain of the primary components,elements, data flows, and processes that may be present in animplementation of an embodiment of the inventive transportation system.As shown in the figure, such a system 200 may include an implementationof the inventive hybrid-electric regional aircraft 202. Aircraft 202includes an embodiment of the hybrid powertrain 203 described herein, apowertrain optimization and control system (POCS) 204, a Flight PathOptimization Platform (FPOP) 205, a flight management system (FMS) 206,and a communications capability 207 for the transfer of messages anddata to other components or processes of the system 200. A regional airtransport operator 210 may include a set of processes for use in flightplanning and other scheduling or administrative tasks related to theoperation of one or more airports and their associated aircraft.Communications capability 207 may be used to transfer data related toaircraft payload, flight path, and energy state (among other parameters)to regional air transport operator 210. Data obtained from and/orprocessed by one or more of the aircraft 202 and transport operator 210may be used to assist in flight scheduling via a regional capacitymanagement platform or process 212, to assist in the administration andscheduling of the “refueling” processes via Recharge-refuel platform214, or to assist in monitoring the operation of the aircraft during andpost-flight (for purposes of pilot logs and diagnosing any issues) via aPOCS online process or platform 216.

As suggested by the figure, demand for the regional air transportservices may be driven by reservations of various types, and by theavailability of aircraft, parts, and pilots. Such information 218 willtypically be used by regional capacity management platform or process212 to determine the appropriate number and type of fights madeavailable to customers. Similarly, a fuel/energy/power services providermay use information related to flight scheduling, fuel needs, availablefuel (such as charged modules), and sales/payments 220 to schedulerefueling operations and accept payments for those operations viaRecharge-refuel platform 214. An aircraft manufacturer 222 willtypically provide information regarding the structure and operation ofthe aircraft and its systems to POCS online process or platform 216 foruse in assisting a pilot or process to operate the aircraft and fordiagnosing issues.

FIG. 3 is a diagram further illustrating certain of the primarycomponents, elements, and processes that may be present in animplementation of an embodiment of the inventive transportation system300. As suggested by the figure, the aircraft and pilot 318 may utilizeone or more systems, platforms, modules, or processes (as suggested by“FMS”, “FPOP” “POCS”, “RRP onsite”) as part of scheduling or operatingthe aircraft. The Recharge-refuel platform onsite 314 (“RRP onsite”)assists the pilot with determining optimal recharge and refuel servicesrequired en route or at the destination by utilizing one or moresystems, platforms, modules, or processes (as suggested by “Recharge andRefuel assistant”, “Service Provider database”, “Preferences”).Alternately, recharge and refuel decisions may be made by the Regionalair transport operator 302 based on information provided to it by theaircraft and pilot 318. The Recharge-refuel platform onsite 314similarly assists with these as shown. Information on recharge andrefuel services requested by the pilot or the operator, and the serviceproviders proposed schedule may be exchanged between the Recharge-refuelplatform online 316 and the aircraft and pilot 318 or regional airtransport operator 302 via a suitable interface 308. Recharge-refuelplatform online 316 may utilize one or more systems, platforms, modules,or processes (as suggested by “service scheduling”, “service calendarand log”, “provider database”, “payment platform, “mapping platform”,etc.) as part of providing recharge and refuel scheduling, processing ofpayments for such services, etc. Similarly, data may be exchangedbetween the Recharge-refuel platform online 316 and the Airport fuelservices provider 306.

As indicated, airports/airfields served by the inventive regionalelectric air transportation system may provide various levels of quickswap and recharge infrastructure to enable high-frequency electricflights. Recharge stations will operate to enable standard and fastcharging of aircraft energy storage units in-situ, while swap stationswill operate to exchange discharged or partially discharged energystorage units and replace them with charged ones. The inventive aircraftincludes bays to house standard and extended energy storage units, andthese may each be modular to enable removal of discrete modulescomprising the standard or extended pack. As a result, the swap mayinvolve replacing the existing modules with a smaller or larger numberbased on operator requirements such as the speed, range, payload andcost of the next flight.

Note that an aircraft's speed, range, payload and operational cost aredetermined to a large extent by the energy storage capacity onboard. Asa result, the ability to add or remove energy supplying modules enablesperformance to be tailored to the needs of a specific flight. Forinstance, on a flight with less than design payload, the operator isable to reduce operating cost and/or increase electric range by addingenergy storage units of weight up to the design payload minus actualpayload, less the reduced fuel required. Conversely, the operator isable to accommodate payloads above design by removing energy storageunits of weight greater than the payload overage plus the additionalfuel required for the flight. This capability enables an operator toreduce costs on legs where the aircraft is loaded to less than capacity,and to accommodate overloaded flights. Further, in order to enableefficient module swaps and recharges, the transportation network may besupported by a software and communications platform 312 that enablespilots or regional air transport operators to determine energy needs andcommunicate these to fuel services providers at the destination airport,or at airport(s) on the way to the destination.

As noted, a block diagram of an embodiment of Recharge-refuel platform304 is shown in FIG. 3. An aspect of its operation is illustrated byFIG. 3(A), which is a flowchart or flow diagram of an example processfor determining recharge or refuel services required at a destinationand in FIG. 3(B) for determining such services on the way to thedestination. These processes or operations are executed by the “Rechargeand Refuel assistant” module or process of the onsite aspects 314 ofplatform 304 based on pilot or operator request.

The processes or process flows illustrated in FIGS. 3(A) and 3(B) dependon multiple factors; these include payload and energy requirements ofthe route leg, onboard energy storage capacity and charge remaining,turnaround time and cost to determine swap and recharge requirements.These parameters and data are typically communicated to the Airport fuelservices provider 306 together with flight details, ETA and turnaroundtime, so that provider 306 can schedule service and make preparations sothat a swap or recharge is performed quickly and properly. To assist thepilot with recharge and refuel at a destination airport, the platform304 determines the additional energy required for the next flight (suchas a flight segment), and generates feasible options based oncapabilities of the preferred service providers at the airport.

Such options may include one or more of tailoring the stored energycapacity to payload, adding stored energy units on low payload flightsfor improved energy efficiency, or removing units on flights whereadditional payload is required. Options may also include swap orrecharge for the stored energy units based on one or more of cost,turnaround time, or impact on operating life of the stored energy units.The options are presented to the pilot along with the cost and timerequired, and the pilot's selection of a desired option is transmittedto provider 306 to schedule services. Similarly, to assist the pilotwith services en route to a destination, platform 304 determines therange of the aircraft given the remaining energy onboard and theadditional energy required for the next leg. This may be done in orderto generate feasible pilot options based on service providers withinrange of the aircraft, along with the cost and time impact of eachchoice. Note that platform 304 may be used to support recharge andrefuel planning for a single flight, for multiple flights in sequence,or for a flight with multiple legs. The sequence of services for amultiple-step trip is selected by the pilot based on guidance from theplatform and transmitted to the service providers. During the course ofthe trip, recharge and refuel needs, and schedule are refreshedperiodically based on progress of the flight, and transmitted to serviceproviders whenever these change significantly or satisfy a specific ruleor condition.

Recharge-Refuel Platform 304 also provides support for billing, paymentsand account management so that such transactions occur efficiently andusing standard transaction authentication, authorization, and processingtechniques. The energy storage units may be owned by the operator of theaircraft, in which case, swap units would be pre-positioned based onflight patterns, much as spare parts are today. The energy storage packscould also be owned by the services provider, or a 3rd party and loanedto the aircraft operator as a service. The services provider stores andrecharges the spare packs, and swaps them as needed for dischargedpacks.

The Recharge-Refuel Platform 304 is comprised of a set of onsitefunctional modules 314 that are implemented onboard the aircraft oron-premises at the regional air transport operator, and a set of onlinefunctional modules 316 accessible via the internet or other suitablecommunications network. Note that although the services provided by anoperator of such a platform will be referred to herein asrecharge/refuel, they may also include an exchange of energy sources,and exchange may entail adding more, or reducing the total number ofbattery packs depending on operational needs. The Recharge-RefuelPlatform connects and permits communications between hybrid-electricaircraft, regional air transport operators, and airport fuel servicesproviders to enable highly efficient fueling operations. Elements of theplatform may include one or more of the following:

-   -   Online service provider database online 320 and onsite 321 is a        periodically updated directory of airports, fuel service        providers at each airport, services capabilities of each        provider, services schedule, pricing and other logistical        details, e.g., affiliations, payment methods supported, etc.        Typically, the most current and comprehensive version of this        database is maintained within online platform 316. Abbreviated        (e.g., locally/regionally customized) versions of the database        are deployed as part of the onsite aspects 314 of platform 304        so that the onsite Recharge and refuel assistant module/process        322 can function without reliance on or connectivity to online        platform 316. However, note that as a backup, one or more of the        distributed sites may also maintain a copy of the comprehensive        version of the database; this redundancy may be of assistance in        providing recharge and refuel data to pilots and regional        facilities in the event of an interruption of services provided        by the central data repository, or to provide a pilot that is        significantly off course with assistance. The abbreviated        versions may be updated periodically from the online database,        when appropriately secure access is available and the updates        can be performed without having an undesirable impact on        operations;    -   Preferences data (elements, processes, or modules 324 and 325)        are a record of tailored settings for an aircraft or operator.        These may include default units, currencies and time zones,        preferred fuel service providers and custom pricing,        communication and transaction processes, as well as standard        fueling protocols for specific routes. These are stored onsite        324, as well as within the online platform 325;    -   Recharge and refuel assistant 322 enables the pilot or the        operator to determine optimal fueling required to support one or        multiple flights, and to select among available providers at an        airport or within range of an aircraft. The function or process        leverages the Provider database onsite 321 and the Preferences        data 324 of the Recharge-Refuel Platform 304, as well as a set        of modules or functions accessible on the aircraft or to an        operator, such as POCS and FPOP (the functions or operations of        which are described in greater detail herein);    -   Service scheduling module 326 receives specific fuel service        requests and attempts to schedule them with the requested        provider. If the requested time slot is available, then the        module returns with a confirmation and records the reservation        on the service calendar 328 for the aircraft. If the time is not        available, then the module returns with alternate openings.        Providers may give control of their schedules to the        Recharge-Refuel Platform, and/or manage schedules themselves.        Where the platform has control, module 326 schedules the service        on the provider's calendar and sends a notification to the        provider. Where the provider has control, module 326 notifies        the provider of the service request and waits for a        confirmation, or details on alternate openings;    -   Service calendar and log module 328 maintains a record of all        services scheduled by aircraft and by provider. For each past        service the module may track disposition, whether the service        was performed, an invoice for the service performed, details on        payments completed, outstanding feedback from the customer, etc.        Module 328 enables service providers to define service slots        available in the future, to permit the platform to book on their        behalf or retain control, to update their calendars to reflect        bookings made outside of the platform, etc.; and    -   Accounts module 330 is a record-keeping and transaction module        that enables providers to issue invoices and enables customers        to make payments. The module leverages standard payment        platforms 332 currently in use by pilots and operators, e.g.,        EDI, credit cards, EFT.

A further aspect of the inventive system 300 is the airport fuelservices provider 306. This represents an operator or manager of anairport or airfield that is part of the inventive transportation system.Such an operator or manager may provide a set of services to enableaircraft to efficiently recharge or swap energy storage units, take onadditional fuel for the range-extending generators, process payments forthose services, etc. Provider of regional airport or airfield services306 may interact and transfer data with Recharge-Refuel Platform 304 viaa suitable interface 310.

Returning to FIG. 3(a), which is a flowchart or flow diagram of anexample process for determining recharge or refuel services required ata destination, in one embodiment, the POCS (described in greater detailwith reference to FIGS. 11 and 12) may be used to determine theavailable energy/fuel for the aircraft, the estimated tine if arrival,and the energy/fuel status after arrival (step or stage 350). Next,based on inputs from the pilot or flight scheduling processes,information or data concerning the next leg or segment of the flight maybe received (step or stage 352). The FPOP process (described in greaterdetail with reference to FIG. 14) is used to determine the total energyrequired for the next leg or segment (step or stage 354). Next, themaximum available stored energy capacity for the next leg or segment isdetermined (step or stage 356).

Preference data (as described with reference to FIG. 3) may then beconsidered to determine the allocation of total energy required for thenext leg or segment between stored (e.g., battery) and generated (e.g.,based on the use of fuel). If such preferences exist (as suggested bythe “Yes” branch of step or stage 358), then such preferences orconditions/constraints are used to determine the recharge and/or refuelrequirements (stage or step 360). If such preferences do not exist (orare for some reason inapplicable, as suggested by the “No” branch ofstage or step 358), then the recharge and/or refuel options may bedetermined based on availability, pricing, etc. (step or stage 362). Assuggested by the figure, this determination may involve considering datacontained in an airport service provider database. The determinedrecharge and/or refuel options may be presented to the pilot, and thepilot's decision(s) received (stage or step 364).

Based on the preferences and/or the pilot's decision(s), the rechargeand/or refueling requirements are communicated to an appropriate serviceprovider 367 (stage or step 366). This may include information regardingthe flight, the aircraft, energy available and needed, the configurationof the energy sources, etc. After receipt and processing, the serviceprovider 367 may provide a confirmation of the recharge and/or refuelorder and any associated information to the pilot (stage or step 368).

Returning to FIG. 3(b), which is a flowchart or flow diagram of anexample process for determining recharge or refuel services en route toa destination, in one embodiment, the POCS (described in greater detailwith reference to FIGS. 11 and 12) may be used to determine theavailable energy/fuel for the aircraft, the estimated tine if arrival,and the energy/fuel status after arrival (step or stage 380). Next, theFPOP process (described in greater detail with reference to FIG. 14) isused to estimate the remaining range of the aircraft and determine thetotal energy required for the next leg or segment (step or stage 382).An airport service provider database may be used as a source ofinformation and data regarding airfields having suitable recharge and/orrefuel facilities (stage or step 384).

Preference data (as described with reference to FIG. 3) may then beconsidered to determine the allocation of total energy required for thenext leg or segment between stored (e.g., battery) and generated (e.g.,based on the use of fuel). If such preferences exist (as suggested bythe “Yes” branch of step or stage 386), then such preferences orconditions/constraints are used to determine the recharge and/or refuelrequirements (stage or step 388). If such preferences do not exist (orare for some reason inapplicable, as suggested by the “No” branch ofstage or step 386), then the recharge and/or refuel options may bedetermined based on consideration of the impact of one or morerecharge/refuel service options on the flight (as suggested by stage orstep 390). This may involve considerations of turnaround time requiredand any expected delays to the flight, costs, airfield fees, etc. Basedon the determined options and the application of any relevant rules,conditions, or constraints, a subset of the possible options may bedetermined and presented to the pilot (as suggested by stages or steps392 and 394), and the pilot's decision(s) received.

Using the FPOP module or process, the aircraft's estimated time ofarrival, stored energy, and available fuel may be determined (stage orstep 396). Based on the preferences and/or the pilot's decision(s), therecharge and/or refueling requirements are communicated to anappropriate service provider 397 (stage or step 398). This may includeinformation regarding the flight, the aircraft, energy available andneeded, the configuration of the energy sources, etc. After receipt andprocessing, the service provider 397 may provide a confirmation of therecharge and/or refuel order and any associated information to the pilot(stage or step 399).

FIG. 4 is a diagram further illustrating certain of the primarycomponents, elements, and processes that may be present in animplementation of an embodiment of the inventive transportation system400. Referring to FIG. 4, in some embodiments, the inventivetransportation system includes hybrid-electric regional aircraft 402,regional tier I or II airports 404, regional air transport operators406, airport fuel services providers 408 and a Recharge-Refuel Platform410.

As suggested by the figure, an embodiment of the inventive aircraft 402may be equipped with a number of modular energy storage units: standardunits 412 sized for use on flights at design payload, and extended units413 for increased electric range on flights at less than design payload.These packs may be positioned for easy swap when on the ground usingquick release mechanisms 414, in locations such as the wings, in podssuspended from the wings, under the fuselage. Aircraft 402 controlsinclude a Powertrain Optimization and Control System (“POCS”, describedin greater detail herein) 416, a Flight Management System (FMS) 417, anda secure datalink 418. The POCS 416 and FMS 417 may be implemented inform of a set of computer/software instructions executed by anelectronic processing element, CPU, state machine, etc. Among otherfunctions, POCS 416 tracks energy storage capacity onboard and energyremaining, FMS 417 estimates arrival times at the destination airport,and the datalink is used for communicating with the operator and fuelservices providers.

The regional tier I or tier II airport 404 is equipped with a swap,refuel and recharge station 420 to enable quick turnaround ofhybrid-electric flights. This includes equipment for automated orsemi-automated removal and replacement of energy storage units,transport of the packs to and from storage, and a storage and rechargefacility for energy storage units. Airport 404 may include a solar farm422 for onsite electricity generation, and onsite grid storage 424 thatis connected to the electric grid 426. Power to recharge energy storageunits may be drawn in an optimal way across the solar farm, the gridstorage and the grid, depending on requirements, cost, availability,etc.

Recharge-refuel platform 410 may connect entities across the air networkto help orchestrate efficient recharges and swaps. The platform isengaged by pilots or air transport operators to identify/selectproviders and services based on operational needs. These requests arerelayed to the providers who confirm and schedule service, and ensurestations are prepared for the arrival of the aircraft. Certain of theoperations or functions that may be performed by platform 410 have beendescribed herein with reference to FIGS. 2 and 3. Regional air transportoperator 406 may operate to schedule and administer services forpassengers, pilots, and aircraft. Certain of the operations or functionsthat may be performed by platform 406 have been described herein withreference to FIGS. 2 and 3. Airport fuel services provider 408 mayoperate to schedule and administer the provision of recharge and swapoperations for the stored energy units (such as elements 412 and 413 inthe figure) or adding fuel for the range-extending generators onboardthe aircraft. Certain of the operations or functions that may beperformed by platform 406 have been described herein with reference toFIGS. 2 and 3.

FIG. 5 is a diagram illustrating an example of the inventiverange-optimized hybrid-electric aircraft 500 that may be used in animplementation of the inventive regional air transport system. In someembodiments, such aircraft and/or air transport system may have one ormore of the following characteristics or qualities, where regionalhybrid-electric aircraft are designed for optimal transport ofpassengers or cargo over regional ranges, typically up to between 500and 1000 miles:

-   -   Aircraft are designed for “lean” operations in-flight and on the        ground, with one or more of the elements or processes described        herein, to enable air operations to small, limited service        airports;        This “lean” operation in-flight is enabled by one or more of the        following features of the aircraft:    -   Lower energy and cost: Aircraft and powertrain are optimized for        regional flights, e.g., lower speed, range and ceiling than        long-haul airliners. A powertrain optimization and control (POCS        or similar) platform is used to optimize energy use during        flights across the one or multiple energy/power sources;    -   Lower ATC load: Onboard ADS-B, including optional datalink to        air traffic control;    -   Fewer pilots: Fly-by-wire capabilities, including (if desired)        auto-land. Comprehensive FMS with operator upload. High levels        of automation including facilities for remote piloting or        fully-autonomous flight;    -   All weather operation: Pressurization for mid-altitude flights        (e.g., 25,000 ft) to enable weather and terrain avoidance; and    -   Minimal runway needs. Balanced field take-off <5,000 ft.        Soft-surface landing capabilities;        In addition, “lean” ground operations are enabled by the        following features on the aircraft, and at the airport:    -   Fast refuel and repair: Air-side quick recharge or swap        capability for onboard energy storage units (e.g., batteries).        Automated or manual transmission of refuel, recharge and        maintenance requirements via datalink ahead of landing;    -   Fast check-in and load: Cabins designed with storage racks near        doors to allow passengers to board with airline standard        carry-on baggage, making up for the low overhead space typical        of small to medium aircraft. Simultaneously, re-configurable        barriers may be used to separate passengers from a secure hold        for storing oversize and checked-in baggage. A simple plane-side        check-in platform (e.g. smartphone, tablet, PC) may enable quick        identity and ticket checks, and fee collection. Design will        support operation even in offline mode without network access,        via prior download of passenger and cargo manifests, and        execution of payments delayed till next covered by a network;    -   Flight prep: Comprehensive FMS with optional operator upload.        Automated system checks performed by POCS or other system.        Onboard aircraft monitoring platform with datalink; and    -   The regional air transport network may be supported by        next-generation capacity management capabilities to help        maximize aircraft load factors and utilization, such as:    -   Higher load factors: Regional reservations platforms, including        links to the GDS for conventional air. The reservations platform        operates to match customer demand in real-time with available        flights, including provisions for fixed and demand-based        scheduling (including near real-time capabilities), on-demand        and charter operations. Operators engage with the platform via        their private ARS (larger operators) or via a variety of hosted,        private labelled ARS offerings (typically used by smaller        operators); and higher aircraft utilization: Virtual “pools” of        electric aircraft may be created, enabling owners and operators        to offer and rent aircraft for short (hours) or medium        (days-weeks) periods of time. Platform enables listing of pooled        aircraft, including availability and rental terms. Platform        includes streamlined processes for locating available aircraft        based on requirements, for negotiating terms and contracting,        payment processing and transfer payments, and to receive or        return aircraft. Similar virtual pools for spare parts and        pilots/crew enable quick turnaround, schedule flexibility.

Returning to FIG. 5, the table(s) below provide a description of theprimary elements of the aircraft illustrated in the figure, and alsonote the difference in construction, materials, and requirements betweenthe inventive aircraft and conventional aircraft.

Figure Required operational Element Description characteristicsDifference from conventional 510 Standard energy storage Bays allow forrapid The modules may occupy the bays with access through energy storagesame location as a traditional the lower wing skin. module swap (<5chemical fuel tank in the main These bays are fully minutes for fullwing. However, a tank is a fully utilized in normal aircraft). sealed,built-in unit which is operation neither accessed nor removable withoutwing disassembly. 511 Extended energy storage Same as 210 Same as 210bays; utilization is optional allowing operators to trade payloadagainst storage capacity, as is traditionally done with fuel 512 Energystorage pods: Pod is designed for Pod is similar to external fuel One ormore energy quick swap capability tanks which have been used storageunits enclosed by (<5 minutes for full extensively by military fighteran aerodynamic fairing, aircraft). Pod is self- aircraft to extend rangebut very mounted externally to the contained, for cooling rarely used oncommercial aircraft, most likely in an and safety aircraft. under-winglocation. requirements, e.g., BMS. 513 Energy storage bay Access same as510. Conventional aircraft may located in the fuselage. utilize fuselagefuel tanks; Bay may be at multiple however, the use of such tankslocations fore and aft for variable CG location is along the fuselage toaid largely lost since fuel is burned in balancing the CG of the off inflight. aircraft. Bay may also be integrated with tracks to slide theenergy storage unit fore and aft to modify CG of the aircraft. 519Chemical fuel tank which Likely none may be located in the fuselage, thewing-body fairing, or may also be located in wing mounted fuel tanks 521Aerodynamic fairing Minimize drag of the The requirement to cover (fairwhich encloses the range generator installation over) the air intakesand/or extending generator (527, while allowing fast exhaust for flightsegments 526), and also access for without generator running isaccommodates air intake maintenance. novel to the hybrid-electricrequirements for Support modular system. Conventional engine combustionand cooling. powertrain capability nacelles have fixed inlets, byallowing different sometimes variable exhaust, fairings for differentand engine is always running in generators. Provide flight. inlet andexhaust for cooling and combustion air. Inlet openings must be whengeneration is not in use to reduce cooling drag. 522 Electric propulsionHigh efficiency Conventional aircraft motors integrated within (>95%),high power propulsors designed to match the propulsor, in this casedensity (>5 kW/kg) engine while the electric motor a ducted fan.electric motor with may be integrated with any maximum continuoussuitable propulsor for the power at 2000-3000 aircraft designrequirements. rpm to match low noise propulsor. Motor capable of peakpower rating up to 2x the continuous rating for limited time duration.523 Quiet ducted fan-this is described in greater detail with referenceto FIG. 6. 525 Electrical distribution system-this is described ingreater detail with reference to FIGS. 7 and 8. 526 Generator andcontroller Generator operates Conventional aircraft engines at >95% andoptimized include a starter-generator for the output RPM combinationwhich starts the of the generation engine, and then absorbs a engine527. Engine small fraction of the engine may be connected to power torun aircraft electrical the generator directly systems. or through agearbox. The hybrid generator may or inverter-controller is may notfunction as the starter, solid state operating and utilizes 100% of theengine at better than 98% power to generate electricity for efficiencyprimary propulsion, and aircraft electrical systems. 527 Range extendingHigh efficiency Large commercial aircraft may generators conversion ofinclude a non-propulsion chemical potential engine, which providesenergy to electrical auxiliary power and power. Engine pressurizationair flow for controlled with a full ground operations, and authoritydigital following loss of a primary engine controller propulsion enginein flight. (FADEC). This generation engine provides energy for primarypropulsion, as well as systems, and operates in combination with storedenergy sources. 528 Ground power charge Provide a single No conventionalequivalent. point: A single access connection point into point on thefuselage the main power which distributes grid distribution bus toenergy to the energy allow simultaneous storage units for charging ofall energy recharging storage units. May also include a connection toprovide active cooling flow to the packs during high-rate chargingoperations. 533 Cockpit, forward High level of cockpit Even highlyautomated aircraft compatible for operation automation to allow requiretwo pilots, and are not by two pilots (or a single for single pilotintended for remotely piloted pilot with ground backup operation withoutoperation. assist), or unmanned for safety compromise. remotely pilotedor Includes the autonomous operations. powertrain interface (POCS) andstandard flight controls and navigation avionics. Additional provisionsfor a single pilot with ground assist, and flight controls which enableremote operation. 534 Powertrain Optimization and Control System (POCS)which serves as the pilot interface to the powertrain and theoptimization processes (and which is more fully described with referenceFIG. 9).

Note that with regards to the embodiment of the inventive aircraft shownin FIG. 5, this embodiment is a conceptual design of a range optimized,regional passenger aircraft. Electricity for the propulsion motors 522is provided by a range-optimized series hybrid-electric powertrain(described further herein with reference to FIGS. 7 and 8), comprised ofenergy storage units 510 and range-extending generators 526-527 (leftside only shown):

-   -   The energy storage units (in this case battery packs) are        located in the wings, including standard packs 510 and extended        packs 511 for use on flights with less than design payload. In        other embodiments, energy storage units may be positioned in        under-wing pods 512, and at various locations within the        fuselage. The embodiment shown has battery packs 513 positioned        under the passenger cabin in the forward fuselage. Fuel for the        range-extending generator is stored in a wing-body fairing tank        519;    -   Propulsion motors 522 in this embodiment are embedded in a        ducted fan 523 for high static thrust to enable short take-off        and landing, high climb rates, and quiet operations. Additional        noise reduction is achieved by locating the fans between the        V-tails 531 and above the fuselage, to shield the ground from        nose. The generators 527 are integrated within noise-insulated        aerodynamic nacelles 521;    -   Power to the propulsion motors is delivered by an electric        distribution system 525 which sources energy from any        combination of the stored energy units 510, 511, 512, 513, and        the range-extending generators 526, 527. Optimal sourcing of        energy from the storage units and generators is managed by the        powertrain optimization and control system 534 (the POCS,        described further herein with reference to FIGS. 9 and 10);    -   The aircraft is “plug-in” hybrid-electric, designed to recharge        stored electrical energy via ground-based charging stations via        a plug-in point 528, or by swapping fully or partially        discharged storage units for charged ones. Charging mechanisms        that connect to the mains or fast charge stations are included        onboard, enabling low or high-rate recharge in-situ. Storage        units are also equipped with quick release mechanisms to enable        fast swaps of storage units or modules thereof. Limited        recharging of storage units by the onboard generators is also        enabled, during low power operations in flight or on the ground;    -   All or most of the aircraft sub-systems may be electric, and        driven by hybrid-electric powertrain. These could include the        flight control system, landing gear, environmental control        systems, anti-icing, fuel pumps, taxi motors, and lighting; and    -   The aircraft may be equipped for a variety of flight modes,        ranging from conventionally piloted, to onboard pilot with        remote assistance, to remotely piloted, to fully autonomous with        remote assistance. As a result, the cockpit of the aircraft 533        may be configured for zero, one or two pilots, and may include        capabilities to enable control of the aircraft by a remote pilot        and by an auto-pilot unit.

An embodiment of the inventive range-optimized hybrid-electric regionaltransport aircraft 500 represents a relatively quieter,forward-compatible hybrid-electric aircraft optimized for regionalpassenger or cargo operations, either manned or unmanned. In someembodiments, such aircraft use a propulsion system powered by one ormore electric motors, delivering thrust via propellers or other suitablemechanism, e.g., ducted fan (such as the inventive “eFan”, described infurther detail with reference to FIG. 6). The aircraft is designed tooperate with high efficiency in regional operations: distances <1,000miles, cruise speeds and altitudes optimized for this range (<M 0.7,<30,000 ft), fuel burn typically 60-80% lower than equivalentconventional aircraft. The aircraft may be smaller (<100 seats) thanconventional jets to match lower passenger volumes on regional routes,designed for shorter runway operations (<5,000 ft) to open up access tolarge numbers of smaller community airports, and operate with low cabinand environmental noise (<70 EPNdB sideline and cabin) for greaterpassenger and community acceptance.

FIG. 6 is a diagram illustrating a variable pitch electric ducted fanintegrated propulsion system 600 that may be used in an embodiment of anelectric-hybrid aircraft that is part of the inventive airtransportation system:

-   -   The propulsion system 600 leverages inventive quiet electric        ducted fan propulsors (referred to herein as an “eFan”) to        enable critical quiet STOL capabilities. Quiet STOL dramatically        improves the ability of an aircraft to fly “close in” to        communities and population centers, thereby delivering a        step-change reduction in passenger or cargo door-door travel        times. STOL enables operations to smaller community airports        (>13,000 in the U.S.), thereby bypassing congested hubs and        saving passengers time. Quiet, efficient, reverse thrust may be        used for ground maneuvering in place of ground support        equipment, reducing the need for personnel and infrastructure,        which may be unavailable at smaller airports. Quiet operation        translates to greater community acceptance, often a limiter for        such flights;    -   As described herein, the inventors propose a novel        range-optimized design with aerodynamics and acoustics optimized        for the intermediate speeds and altitudes of the regional        hybrid-electric aircraft, emphasizing high efficiency in cruise        and high static thrust for STOL. This is enabled by use of a        low-pressure ratio (1.02 to 1.10) variable pitch fan, enabling        tailoring of propeller blade pitch to flight mode, including        reverse thrust, regenerative braking and feathering;    -   The eFan is powered by one or more high-power-density electric        motors located at the centre of the duct and connected to the        fan directly, or through an optional reduction drive. Liquid or        air cooling of the motors is fully integrated within the duct.        The transmission is fault tolerant, designed for continued safe        operation in event of motor, sensor or communication faults,        which either preserve, or allow for graceful degradation of        thrust output;    -   In addition to enabling the graceful degradation of thrust, the        variable pitch electric fan enables additional safety and        efficiency benefits not easily attained with conventional        propulsion systems and methods. The available high torque, high        response rate of thrust variation may be applied for        supplemental flight control, enhancing efficiency, and may        augment or replace flight controls completely (for example in        case of primary control failure);    -   In normal operation, control of the propulsor is via pilot or        auto-pilot commanding % power, % reverse power or % regenerative        braking, which are translated by the POCS system into        appropriate Propeller(s) blade pitch angles, Motor(s) RPM and        torque (or regenerative RPM and torque), and transmitted to the        motor and variable pitch controllers. In backup mode POCS        automation is bypassed, and the pilot commands the motor and        variable pitch controllers directly:        -   The POCS system translates % full-power to RPM, torque and            Propeller blade pitch angle based on the Power plan, %            power, Flight Mode, altitude and speed. For multiple            propulsors, commands may be synchronized, so all coupled            propulsors operate with the same settings;        -   Similarly, the POCS system translates % regenerative braking            or % reverse power to matching Propeller blade pitch angles            with motor set to appropriate levels of regenerative RPM and            torque; and        -   In case of emergency shutdown, the POCS system (or pilot            directly via the backup mode) commands the propeller blades            to feather position and halts motor motion.    -   The high torque at low RPM of the electric motors coupled with        the high static thrust of the ducted fan leads to good STOL        performance while the combination of low fan tip speeds,        fan-stator and duct acoustic design and duct acoustic treatments        deliver significantly lower noise signatures. As an added        benefit, the increased safety and “jet like” appearance of the        ducted fan are expected to translate to strong consumer appeal        relative to open propeller aircraft often used for regional        flights;    -   The propulsor is designed for forward-compatibility targeting        optimal efficiencies over a 30% higher speed band, with        structures designed to accommodate the higher torque and        gyroscopic loads of future motors;    -   Range-optimized design tailored for high cruise efficiency at        intermediate speeds and altitudes typical of regional operations        (Mach <0.7, Altitude <30,000 ft);        -   Forward-compatible design by selection of mass flow design            points over a cruise range that includes future maximum            speed and altitudes. This range extends from 30 to 250 mph            in equivalent airspeed, at Mach numbers <0.7. Fan cruise            pressure ratio is much lower, 1.02-1.10 relative to            high-speed jet engines for high net installed efficiency,            especially in climbs and lower altitude, lower speed cruise            operations. Inlet and exhaust areas are selected to avoid            separation and distortion over this range of mass flow            conditions; and    -   Variable pitch fan disk and blades 601 to enable high efficiency        over the targeted speed range.

In some embodiments, the eFan design consists of:

-   -   A fan disk with a plurality of fan blades (6-20 blades), and a        disk solidity in excess of 60%;    -   Fan blades designed for high efficiency at low pressure ratios        and operation at 3000-4000 RPM. This entails an increasing        aerodynamic loading with span, and corresponding increase in        chord;    -   Fan tips may be a spherical cross section to allow variation of        pitch within the matching duct wall contour while maintaining        the small tip clearance required for high efficiency; and    -   Fan blades designed for optimal efficiency over the targeted        cruise speeds, extending to future maximum speeds and altitudes.        Including design for static thrust, reverse thrust and        regenerative braking via the variable pitch capability;    -   Fan blades are mechanically pitched over a wide range of angles.        Fan pitch angle is measured such that 0° aligns the blade tip        chord plane with the plane of rotation;    -   Fan blades are variable pitch with angle change at speeds        >100°/sec;        -   At minimum, the variable pitch mechanism will accommodate            the normal operating range between 15° for fine pitch on            takeoff, up to 50° in high speed, low RPM cruise;        -   Maximum positive angle may be up to 80° for the “feathered”            position of minimum drag, as blades are aligned with            incoming flow; and        -   Minimum angle may be up to -40° to enable reverse thrust            while maintaining continuous motor and fan rotation.

As shown in FIG. 6, fan blades 601 are attached at the root 611 to amechanical hub with a mechanism 610 for electro-mechanical variation ofblade angle (pitch) from a negative angle providing reverse thrust forenhanced runway braking, to a fully streamlined angle for minimum dragin case of propulsor shut-down in flight. The entire mechanism rotateswith the fan disk and electric drive motor. Blade pitch change signal ispassed across the rotating boundary. A mechanism drives all of theblades simultaneously through a mechanical linkage. The design includesa no-back, directional brake to lock out feedback torque from themechanism during periods of no pitch change.

The eFan may be installed in an aerodynamically contoured flow duct 603to deliver the noise reduction and static thrust required for quiet STOLoperations. In one embodiment, the duct axial length is 50-125% ofdiameter, with the fan located at 40-60% of duct length. The duct issupported by a plurality of stators 602 located behind the fan disk. Theduct inlet lip contour 604 is of continuously variable radius designedfor high efficiency in cruise, no separation at low speeds and highpower, and reduced propagation of forward fan tones. The duct inlet lipcontour 604 ahead of the fan promotes laminar flow while minimizingseparation. The duct contour aft of fan is sufficiently gradual to avoidflow separation in the normal operating envelope. The duct exit areaminimizes jet noise by expanding flow aft of fan, reducing flow to nearfree stream levels. The duct outer contour 603 is designed to maximizenatural laminar flow for low drag. The duct internal cross-section mayinclude a radial recess or other mechanism aligned with the fan toenable the small tip clearance required for high efficiency.

The inventive eFan 600 may be characterized by one or more of thefollowing:

-   -   It is designed for low-noise operation, with 15-25 EPNdB lower        noise than conventional aircraft, as enabled by one or more of        the following features:        -   Shorter blades in ducted fan relative to an equivalent            thrust open propeller translate to quieter operation due to            reduced tip speeds, target 500-600 fps, upper limit of 800            fps, and attenuation of radial noise components by the duct            and duct insulation. In addition, blades are optimized for            low noise including leading edge sweep angle, trailing edge            shape, blade tip and root shapes, and blade tip to duct            clearance shape with varying pitch;        -   Rotor-stator noise reduction via stator design and placement            for low noise        -   The number of stators is optimized for noise and determined            by number of fan blades and blade rpm to ensure primary, and            secondary BPF fall below 2500 Hz. (BPF=blade passage            frequency);        -   The stator spacing behind blades is optimized for noise            reduction, 1.5 to 2.5 blade chords aft of the fan. The            stator twist and platform is designed to remove flow swirl            to reduce turbulent eddy noise;        -   Use of variable pitch blades reduces wake intensity, the            main driver in rotor-stator noise, especially at takeoff;        -   The duct is designed to attenuate noise, including optimized            axial location of the fan in duct, design of duct lateral            profile, inlet lip contour and exit profile to minimize            propagation of fan tones, acoustic treatments of critical            areas of the duct inlet, central fairing, and outlet; and        -   The duct may be used as a variable drag air brake, replacing            conventional spoilers which are a significant source of            airframe noise;    -   It is designed for energy recovery and aircraft speed control        via regenerative braking to improve overall efficiency, and to        eliminate the need for a typically noisy air brake mechanism.        Regeneration, and hence airspeed control, is fully variable, and        is enabled by adjustment of variable pitch propellers and the        electrical load applied to the motors. A pilot may request %        regenerative braking using the standard power lever angle,        moving into a guarded range below standard flight idle. The POCS        system delivers % regenerative braking by controlling propeller        blade pitch angles and motor regenerative power output to        deliver target levels of aerodynamic drag measured via motor        power output;    -   It is designed for reverse thrust for reduced stopping        distances, especially on surfaces with reduced braking action,        and also for ground operations requiring reverse (e.g., standard        gate “push-back”), reducing need for airport operations        infrastructure. Reverse thrust may be enabled though a variable        pitch fan with the blades pitched to a negative angle, or may be        enabled by reversing the motor direction of rotation. Reversed        rotation is a capability unique to the electric fan, not        available with a conventional aircraft engine without        complicated gearing;    -   It is designed for aircraft supplemental or primary control. The        high constant torque, millisecond fast motor response, and high        speed fan pitch rate response enable the ducted fan to quickly        change thrust output. This differential or vectored thrust        produces moments around the aircraft center of gravity which may        be utilized to provide primary or supplemental aircraft control.        In case of primary control failure, control system may be        reconfigured to utilize thrust moments to restore some degree of        lost control authority:        -   Differential thrust. In one implementation, the thrust from            one or more propulsors may be varied to provide a moment            around the center of gravity. Depending on motor location,            and number of propulsors, this may produce a pitch or yawing            moment;        -   Vectored thrust. In a more active implementation, thrust            from one or more propulsors may be vectored through use of            exhaust louvers, propulsor gimbals, or other means to            produce a pitch, yaw, or rolling moment;    -   Ducted fan may be designed for lift augmentation either        directly, in which thrust from one or more propulsors is        vectored through louvers, gimbaled mounting or other means in        order to generate a thrust vector which directly offsets        aircraft weight (i.e. lift), or indirectly, by channeling        exhaust flow over aerodynamic surfaces to produce suction        (lift), and/or flow deflection (e.g., Coanda surfaces such as a        “blown flap”);    -   It is designed for integrated cooling. Electric motors and the        related controller-inverter electronics produce a significant        amount of waste heat. It is highly desirable that heat rejection        be accomplished with minimal added weight and drag. This may be        implemented directly into the ducted fan design in the following        manner;        -   Heat exchanger surfaces may be incorporated into the            stators, and/or the inner, aft surface of the duct. In this            way, there is no additional radiator and no additional            surface area for drag, especially important since heat flow            varies directly with power output, and may drop to zero in            flight during descent, at which time cooling penalty is            desired to be negligible;        -   Motor heat may be rejected to a heat exchanger in the            leading edge of the nacelle to prevent ice buildup when            flying in freezing precipitation; substantially more energy            efficient than providing power to an electro-thermal hot            leading edge;    -   Note that the eFan design is a fault-tolerant architecture, as        exemplified by the following features:        -   The assembly is designed to ensure continued safe operation            with graceful degradation of thrust in the event of a fault            in any one motor system (including motor inverter,            controller, power bus etc.), as enabled by POCS (element            1042 of FIG. 10 and/or element 1160 of FIG. 11). Hardware            designed to support graceful thrust degradation, including            multiple electric motors may power a single shaft,            electrical isolation ensures that a fault in one does not            affect safe operation of the other(s), and individual motors            may be designed for peak performance 60-80% above continuous            for recovery periods of 5-10 minutes, so that surviving            motors are able to power up to partially or fully            accommodate faults elsewhere. This may include designing the            motor for higher power ratings and introducing mechanisms            for aggressive cooling of hot spots, so that extended            peaking does not damage the motor. In the event of a loss of            motor power due to a motor fault, the POCS alerts the pilot            and redistributes power to the healthy units to preserve            thrust for sufficient time durations to allow the pilot to            manoeuvre to safety (element 1144 of FIG. 11);        -   In case of the total failure of a propulsor, including            failure due to physical damage, blades may automatically be            set to “pinwheel” (blades continue to rotate, but no energy            extracted from the flow for minimum drag), or pitched to a            fully streamlined angle (“feathered”) and the motor then            braked to prevent any rotation. Failure or potential failure            may be detected through monitoring of the motor power output            vs. commanded output, and by monitoring vibration at the            motor to detect mechanical damage/failure; and        -   Fault tolerance in event of communications or sensor            failures may be achieved via redundant systems. Standard            connection of the motor and variable pitch controllers to            POCS is supplemented by back-up wiring, including capability            for direct access to the controllers without POCS            intervention. Similarly, motor and pitch sensors are            supplemented by back-up sensors or a sensor-less control            capability. The sensor fault detection capability within            POCS switches across these as required.

Returning to FIG. 6, the table below provides a description of theprimary elements of the eFan illustrated in the figure, and also notethe difference in construction, materials, and requirements between theinventive eFan and conventional fans/propulsers.

Required operational Difference from Figure Description characteristicsconventional 601 Low pressure, variable Fan blade pitch rangeConventional turbofan pitch fan with 6-20 blades, from 15 to 50 degreesblades are fixed pitch, high a disk solidity of >60%, (normaloperations), up pressure ratio (1.4 to 1.8) and pressure ratio of 1.02to 80 degrees (feather), and disk solidity >1 to 1.10 and −40 degrees(reverse thrust), cruise efficiency >95%, cruise pressure ratio <1.10602 Stators aft of the fan Low noise operation; Fan: stator noise removethe swirl from the fundamental blade interaction is significantly flow,reducing turbulence passage frequency different (and less losses, andsupport the <2500 Hz, External noise dominant) with duct allowing a verysmall <70 EPNdB at 500 ft conventional high fan tip clearance. Statorssideline takeoff pressure fan may also function as a measurement.radiator with embedded cooling fluid coils. 603 Ducted fan nacelle whichOuter surface designed Conventional jet nacelles minimizes external andfor minimum provide a substantially internal drag. Nacelle aerodynamicdrag, with different flow contours, length optimized to meet up to 50%laminar flow, both internal and external requirements in at Mach numbers<0.7 performance, noise Internal contour to attenuation, weight, andminimize drag, attenuate drag, and may range from fan tonal noise, and50% to 125% of diameter maximize thrust generation efficiency. Internalcontour may preserve free stream velocity or allow flow acceleration.604 Nacelle leading edge Leading edge radius Conventional turbofansufficient to prevent nacelles compromise static separation at highpower, thrust for cruise at high low speed operations Mach number. Ice(high static thrust) while protection uses hot bleed providing low dragin air from the high pressure cruise, including pressure turbine.gradients favorable to natural laminar flow. Leading edge thermallyheated for ice protection. 610 One or more electric Energy density >5n/a motors kW/kg continuous rating, with peak power at <4000 rpm 611Variable pitch hub Fast (>100 deg/sec) Conventional turbofans aresimultaneous adjustment fixed pitch. of blade pitch angle from extremenegative to extreme positive.

FIG. 7 is a diagram illustrating a powertrain 700 and its associatedelements that may be used in an embodiment of an electric-hybridaircraft used as part of the inventive air transportation system. Asshown in the figure, in one embodiment the powertrain 700 and associatedelements may include or be characterized by one or more of the followingfeatures, elements, processes, or aspects:

-   -   A series hybrid-electric powertrain delivering power via one or        more electric motors, combining batteries (or other method(s)        for storing electrical energy) with a chemical fuel based engine        and generator combination as an optional range extender. The        engine could be piston, turbine or other form of heat engine to        convert stored chemical energy to electricity. The powertrain        also delivers power to other electric sub-systems of the        aircraft which could include the flight control system with        electric actuators, electrically actuated landing gear,        environmental control systems, taxi motors, anti-ice, fuel        pumps, and lighting;    -   The powertrain comprises a set of modules, e.g., battery packs,        engine, generator, power inverters DC/DC converters, fuel        system, electric motors, etc. integrated via a powertrain        platform comprising power and control circuits. Each module is        connected via a control circuit to the powertrain optimization        and control system (POCS). Module controllers are queried or        directed by the POCS platform, and transmit a range of state and        performance information to POCS on-demand or continuously. POCS        to module controller communication is enabled by APIs, defining        protocols by which POCS and modules communicate;    -   The operation of the powertrain is controlled by POCS based on        pilot direction, in semi-automated or fully-automated mode(s).        To enable this, individual powertrain modules are equipped with        controllers that communicate with POCS across the module        interface via APIs, on-demand and/or periodically. Key metrics        communicated to POCS may include the following: on-off, RPM,        power, status for each motor; battery capacity, power, status        for each battery pack; fuel level and flow rate; engine on-off,        power, status; and status for each converter. Key control        directives received from POCS include the following: on-off, RPM        and torque for each motor; power for each battery pack; on-off        and power for the engine; and    -   The powertrain is “plug-in” and designed to recharge stored        electrical energy via ground-based charging stations. Limited        recharging in flight may also be enabled: by the engine during        low power operations; and/or by means of regenerative braking of        wind-milling propulsors during descent and of landing gear        following touchdown. As noted, energy storage units may be        contained in multiple modules, installed internal or external to        the aircraft, for example in the wings, with an optional quick        release mechanism to enable fast swap or jettisoning. Included        onboard are charging and cooling mechanisms that connect to the        mains or fast charge station for low or high-rate recharge        in-situ.

Referring to FIG. 7, the powertrain 700 includes one or more electricpropulsors 701, one or multiple distribution buses 730, one or morerechargeable energy storage units 710 and if desired, one or moreoptional range-extending generators 720. The powertrain 700 may alsoinclude element 731 to power the distribution buses 730 from an externalsource, element 713 to charge the rechargeable storage units 710 from anexternal source, and element 732 to distribute power to other electricsystems of the aircraft. Note that elements 713, 731, and 732 may takeany suitable form, such as (but not limited to) an electrical interface,a cable, a coupling, or a controller. Whatever its form, element 732typically includes one or more DC-to-DC converters to convert power tothe lower voltage levels typically required by the other electricsystems, e.g., environmental control systems, fuel pumps, anti-icing,lighting, as well as back-up/fail-safe distribution for vital systems,e.g., flight controls and avionics.

Powertrain 700 is a plug-in series hybrid designed to power the electricpropulsors 701 with energy drawn optimally from the rechargeable energystorage 710 and the range-extending generators 720. Given the typicallylower total cost of energy from rechargeable energy storage 710, poweris drawn from the range-extending generators 720 only if stored energyis insufficient to complete the flight, or if maneuvering requires powerbeyond that available from the rechargeable storage 710. The total costof energy from the rechargeable energy storage units equals the cost ofthe energy used to charge the units, the efficiency of charge anddischarge of the units, and the cost of the units amortized over theirusable life, defined as number of charge-discharge cycles beforeperformance degrades below a threshold. Cost effective battery packs,for instance, can be charged using low-cost electricity from the grid,and offer very high efficiency charges and discharges, with a usablelife of >1,000 cycles.

Electric propulsors 701 are either ducted fans as shown (such as thosedescribed with reference to FIG. 6), or open propellers. The propulsorsare designed for operation in multiple modes through the variable pitchmechanism 703 shown, or by other means such as an adjustable exhaustplug. The operational modes enabled could include take-off, cruise,regenerative braking, feathering, reverse thrust, for example. Fan 702is mechanically coupled to one or more electric motors 704, with amechanism or process to isolate individual motors to enable continuedoperation in the event of mechanical or electrical faults. In normaloperation, fan 703 is driven by electric motors 704, which receiveelectric energy from the distribution bus 730 via the motor controllerand DC-AC inverter-rectifier 705. In regenerative breaking, on the otherhand, fan 703 drives the electric motors 704 to generate electric energythat is delivered to the distribution bus 730 via the DC-ACinverter-rectifier 705.

Rechargeable energy storage units 710 are comprised of battery packs 711shown, supercapacitors, or other media for storing electrical energy (ora combination thereof), coupled with a battery management system(s) 712that manages operation and safety of the packs. Each pack may compriseof multiple individually removable battery modules, and operate eitherwith some or all of these modules in place. Storage units 711 arecharged primarily by external sources via 713, but also enable limitedcharging in flight, by the electric propulsors 701 during regenerativebraking, or by the range-extending generators 720 during low-powerflights. The rechargeable storage units 710 deliver power to thedistribution buses 730 when discharging, or receive power from thedistribution buses 730 or external source 713 when recharging.

Storage units 711 are equipped for fast charge in-situ via externalsources 713, and also equipped for fast swap with quick releasemechanisms. These enable a manual or automated swap of on-board storageunits with pre-charged replacements positioned on the ground.

The optional range-extending generators 720 may be comprised of internalcombustion engines 721, each driving one or more generators 723.Alternately, these could be comprised of units that convert storedchemical energy directly to electricity, e.g., hydrogen fuel cells. Theinternal combustion engine 721 may be a conventional one, using one of arange of fuels, e.g., diesel, gasoline, jet-A, for initiating andsustaining combustion in one or more combustion chambers. The fuel isstored in one or more fuel tanks 722, and pumped to the generators asneeded. The engine 721 is mechanically connected to the generators 723,typically with a mechanism or process for isolating individualgenerators in the event of a fault. When operating, engine 721 drivesthe generators 723 to deliver electric energy to the distribution bus730 via AC-DC rectifiers or inverters acting as active rectifiers 724.

FIG. 8 is a schematic of a series hybrid drive configuration 800 for arepresentative aircraft that may be used in implementing an embodimentof the inventive transportation system. Note the following features,elements, processes, or aspects:

-   -   The powertrain includes two electric propulsors 801, each        powered by two electric motors 802, two battery packs as        rechargeable storage units 803, and a single range-extending        generator. In this example, the generator couples a single        internal combustion engine 804 coupled with two motor generators        805;    -   In some embodiments the electric motors 802 are >90% efficiency        brushless, electronically controlled axial-flux drive motors,        with specific power density >5 kW/kg at continuous output power,        and peak power output >50% above continuous output. In addition,        the motors may be designed for low RPMs, e.g., <4,000 to enable        direct drive. The motor generators 805 are of the same        architecture as the drive motors, able to operate at peak for a        recovery period, e.g., failure of a battery pack. Each motor 802        and generator 805 is coupled to a solid state        convertor-controller (such as a rectifier), to provide precise        motor control with minimal loss and to protect the motors from        voltage fluctuations;    -   In one embodiment, the internal combustion engine 804 is a        turbo-diesel piston engine, tuned to operate with maximum        efficiency at a fixed RPM that may align with the design RPM of        the electric motors to enable direct drive. The turbo-charging        allows the engine to deliver relatively uniform power from sea        level up to 10,000 ft;    -   Power is delivered to each of the propulsors 801 by one of two        primary buses 806, each of which is powered by one of the two        battery packs 803, and one of the two motor generators 805. The        primary buses 806 also distribute power to the non-propulsion        sub-systems of the aircraft 810, via step-down DC-DC convertors        807;    -   A third vital bus 808 re-routes power to accommodate failures of        any of the electric motors, distribution buses, battery packs or        generator. In the event of failure of an electric motor 802, the        vital bus 808 re-routes power to the surviving motors, enabling        the pilot to request peak thrust for recovery maneuvers. In        event of failure of a primary bus 806, the vital bus 808 engages        to fully replace the lost functionality. In event of failure of        a battery pack 803 or generator 805, the vital bus 808 re-routes        power from surviving sources to maintain balanced output from        the electric motors; and    -   The vital bus 808 also re-routes power to the non-propulsion        sub-systems 810 and avionics 812 in the event of failure of a        primary bus 806 or one of the step-down DC-DC convertors 807.    -   810 and 812 shown are representative of standard circuits used        to power non-propulsion sub-systems and avionics onboard an        aircraft. The former includes systems such as Ice protection,        the Fuel pump, Pressurization, Cooling, Flight controls, and        operates at an intermediate voltage, e.g., 270V. The latter        operates at a low voltage, e.g., 28V, and includes the most        critical avionics systems on an aircraft. As shown, these        circuits typically include redundant paths and additional power        sources for fault tolerance in the event of failures.

As described with reference to FIG. 5, the inventive transportationsystem includes an aircraft design optimized for maximum transportefficiency over regional ranges, in particular, the innovativerange-optimized hybrid-electric powertrain. In some embodiments, thisdesign goal contributes to the following features, which collectivelyenable a 65-80% lower DOC over targeted regional ranges thanconventional aircraft:

-   -   A powertrain sized for maximum transport efficiency over        regional ranges <1,000 miles, designed via a 3-level or 3-tier        objective:        -   (A) Highest efficiency (80+% lower DOC than conventional            aircraft) and optimal speed over electric-only range;        -   (B) Intermediate efficiency (60-70% lower DOC than            conventional aircraft) and optimal speed over larger hybrid            range; and        -   (C) Good efficiency (30-60% lower DOC than conventional            aircraft) and lower speeds beyond to maximum range            determined by onboard stored energy and fuel less safety            reserves;    -   A powertrain sized for speeds and altitudes that are optimal for        regional sub-range (B), determined by minimizing an objective        function, for example “DOC+I+COT” for flights over the sub-range        (may also be optimized for lower speeds over the regional        sub-range (C) based on the relative frequency of travel over        range (C) versus ranges (A) and (B)). This leads to design for        slower speeds, lower altitudes and shorter ranges than that of        conventional jet aircraft;    -   A rechargeable energy storage and range-extending generator        combination, sized based on speed and range requirements        (A), (B) and (C). Stored energy-first design, whereby        rechargeable energy storage is fully depleted for flights in        ranges (B) and (C) with required reserve maintained as fuel for        the optional range-extending generators, or less required        reserve if no range-extending generators are on board.        Rechargeable energy storage and range-extending generators sized        to enable optimal speeds over hybrid range (B), and rechargeable        energy storage sized to enable optimal speeds over electric-only        range (A). Range-extending generators sized to enable        lower-speed cruise over range (C), and therefore downsized to        under 70% of maximum continuous powertrain output (much lower        than conventional aircraft) for improved efficiency; and    -   Optimized energy storage mass, 12-20% of the aircraft weight,        and downsized range-extending generator, with very low power        output, typically less than 70% of maximum continuous output of        powertrain (lower than a conventional aircraft).

Note that a design process for an embodiment of the inventiverange-optimized aircraft and powertrain is described herein, including aprocess by which the noted 3-tier set of speed and range requirements isused to size elements of the hybrid-electric powertrain. The describeddesigns for the inventive aircraft and associated elements are forwardcompatible to support anticipated upgrades of operating capabilities orkey powertrain modules over the life of the airframe. Given the rapidevolution of EV technologies, this feature ensures that the powertrainremains competitive over time as individual module technologies improve,e.g., batteries, supercapacitors, electric motors, internal combustionengines, fuel cells. In addition, this feature enables the aircraft totransition smoothly from hybrid-electric to all-electric once energystorage technologies improve to the point where range-extendinggenerators are no longer required.

To provide forward compatibility, the powertrain is designed by sizingthe energy storage units and generator combination for the speed andrange requirements (A), (B) and (C) mentioned, based on technologiesavailable at aircraft launch and forecast to be available over the 15year period beyond (including planning for transition fromhybrid-electric to all-electric). This leads to a forecast for onboardrechargeable storage and range-extending generators, and in turn,determines performance characteristics over time: speeds, electric andhybrid-ranges and operating costs; with electric-ranges increasing andoperating costs decreasing as technologies improve.

Forward compatibility may require limiting the weight of therechargeable energy storage units to 12-20% of the aircraft weight sothat payload capacity is roughly uniform as EV technologies improve.Higher weight fractions would lead to designs that are larger andheavier than aircraft of similar payload in the initial years, withpayload increasing over time. Lower fractions lead to suboptimalefficiencies given much higher use of range-extending generators.

To achieve forward compatibility, the powertrain platform is designed tosupport module technologies over the design life of the airframe(typically 15-20 years). This can be realized by designing the platformbased on powertrain operation with future modules where appropriate, andensuring upgrades required to accommodate future technologies arerelatively simple and cost effective. For instance, wiring to theelectric motors may be rated up to 30% higher peak power, to supportmore powerful motors and higher aircraft speeds in the future. Wiring ofthe platform may be designed to allow upsizing and redistribution of therechargeable storage units, downsizing or removal of the range-extendinggenerators. Wiring from the energy storage units may be designed tosupport higher capacity packs in the future, and space used for therange-extending generators may be wired for use with rechargeablestorage units when the generators are removed. In addition, modules andelements of the powertrain e.g., wiring, harnesses, switches,converters, that will likely require upgrade are designed and positionedfor simple replacement and easy access.

The powertrain platform and the powertrain optimization and controlsystem (POCS, described with reference to FIGS. 9-11 and the examplepowertrain configurations illustrated in FIG. 7-8) are designed toenable a staged transition of the powertrain from hybrid to all-electricas storage technologies improve. This includes design for operation withor without the optional range-extending generators, fuel or rechargeablestorage based reserves, and a platform designed to allow the swap ofgenerators with storage units over time. In addition, the powertrain maybe characterized by the following:

-   -   Modularity—a set of swappable nearly “plug and play” capable        modules connected by a hardware and software platform. This        enables the powertrain to accommodate rapidly improving        technologies via relatively simple upgrades of the modules.        Powertrain modules may include the rechargeable storage units,        range-extending generators and electric motors. The powertrain        platform includes the powertrain optimization and control system        (POCS), electrical wiring, distribution buses, convertors, fuel        system, sensors, cooling, shielding, and any additional        processes or structure that operate to enable the modules to        cooperate to form the powertrain;    -   Modularity is facilitated by design of the powertrain platform        and the interfaces that connect the modules to the platform to        be compatible with the range of module technologies that are        likely to be available over the life of the airframe (as        mentioned previously). This enables compatible modules to be        plugged into the powertrain by connecting the module to the        interfaces, comprised of electrical and control circuits, and        services such as cooling, shielding, fuel, and structure. For        instance, range-extending generators plug-in to the platform via        electrical connectors to the generator rectifiers, via POCS        connectors to the generator controllers, the internal combustion        engine controller and the fuel system controller, and via fuel        and cooling services to the generators and engine. In areas        where upgrades may be required to accommodate a new module, the        powertrain is designed to enable relatively simple and        cost-effective modification;    -   Individual module controllers are connected to the powertrain        optimization and control system (POCS) to orchestrate operation        of the powertrain. Module controllers are queried or directed by        the POCS platform, and transmit a range of state and performance        information/data to POCS on-demand or continuously. POCS to        module controller communication is enabled by APIs, defining        protocols by which POCS and modules communicate. The operation        of the powertrain is controlled by the POCS based on pilot        direction, in semi-automated or fully-automated modes. To enable        this, individual powertrain modules are equipped with        controllers that communicate with POCS across the module        interface via APIs, on-demand and periodically. Key metrics        communicated to POCS may include the following: on-off, RPM,        power/status for each motor; battery capacity, power/status for        each battery pack; fuel level and flow rate; and generator        on-off, power/status. Key control directives received from POCS        may include the following: on-off, RPM and torque for each        motor; power for each battery pack; and on-off and power for the        generator;    -   The powertrain is designed to support relatively simple module        exchanges/swaps. The powertrain platform and interfaces to the        platform, electrical, control, and services such as cooling,        shielding, fuel, structure, are designed to accommodate a wide        variety of modules. These include specification of corresponding        wiring, control or monitoring and other service capabilities        onboard each module to enable a type of “plug and play” pairing.        For instance, in the case of battery packs, this would typically        include peak and steady-state discharge rates, BMS protocols,        socket descriptions. POCS also enables calibration of the        powertrain following module changes. This may include FAA        certification of the powertrain for use with a range of        pre-approved compatible modules. Further, in some cases, the        design of the powertrain may include the ability to support        relatively simple or cost-effective modification in areas where        new modules may require modification;    -   Powertrain variants may be implemented that have performance        tailored to different markets; in some cases this may be done by        altering the choice of powertrain modules, to offer different        speeds, ranges and operating costs for an aircraft        configuration. For example, an “economy” commuter powertrain        might couple a highly efficient turbo-diesel range extender with        moderate density batteries, offering best-in-class operating        costs but long flight times for longer ranges. In contrast, a        “performance” business powertrain might couple a less efficient        but lighter turbo-shaft range extender with higher density        batteries, offering best-in-class regional speeds but at        modestly higher operating costs;    -   The powertrain operation may provide optimal efficiency over        regional ranges via maximized use of the rechargeable storage        units; this may be implemented by targeting full depletion        during a flight (or lower if within electric range (A)), with        range-extending generators switched on only if the available        stored energy is insufficient to complete the flight. This        translates to ultra-efficient stored energy flights within the        electric-only range (A), and very efficient hybrid flights over        the longer hybrid range (B) or total range (C);    -   Safety reserves are maintained across the rechargeable storage        units and the range-extending generators to maximize use of the        rechargeable storage units. For example, if the power output of        the onboard range-extending generators enables safe maneuvering        of the aircraft, then reserves are maintained as fuel for the        generators sufficient for operation for a length of time        determined by regulation or by other means. If range-extending        generators do not enable safe maneuvering of the aircraft, then        the fuel reserves are supplemented by stored energy equivalent        to that required to enable maneuvering over the target length of        time;    -   The powertrain is “plug-in” and the rechargeable storage units        are designed to be replenished by ground-based charging        stations. This is enabled by an onboard charging platform for        connecting to the mains or to a fast charge station for low or        high-rate recharge in-situ. Also included are fast swap        capabilities for the rechargeable storage units via release        mechanisms to enable quick replacement of depleted units with        charged ones;    -   Each rechargeable storage unit may be comprised of multiple        individually swappable modules. This enables increased        efficiency on low payload flights by loading additional modules        to extend the electric-only range. Or unloading some modules to        increase payload capacity, but at loss of electric-only range.        In case of batteries, this is enabled by design of cell modules        that plug into bays within a battery pack. Each module may        contain one or many cells with wiring, sensors and controllers,        along with first-level cooling, structural support and fire        protection features. Easy installation is enabled by connectors        to the battery pack power, sensor, control and cooling circuits,        and by quick release mechanisms; and    -   The powertrain design provides energy recovery via regenerative        braking of the propulsors. To enable this, propulsors are        equipped for varying degrees of air braking through use of a        variable pitch propeller or another mechanism, e.g., adjustable        exhaust plug. As a result, the rechargeable energy storage        receives energy from electric motors operating as a generator        when air braking is engaged. The powertrain is also designed for        selective charging by the range-extending generator during low        power operations. In this mode, some or all of the electrical        energy generated by the range-extending generator is directed to        the rechargeable energy storage units.

The inventive powertrain designs and configurations are architected topermit graceful degradation, for safety and fault tolerance exceedingstringent aviation requirements (FAA and EASA). This includes ability totolerate failures in power sources (energy storage units, generators),motors (propulsion, generator), convertors (inverters, rectifiers, DC-DCconvertors), distribution (buses. wiring), controls (sensors,communication), as well as safety in event of moderate or severe impacton the system.

To achieve this, the powertrain is designed for graceful degradation,whereby failure in any area has no more than a fractional impact on theperformance of the powertrain, allowing near normal flight to a nearbyairport for repair. At least three unique aspects of the inventivehybrid powertrain enable this, with only a modest cost or weightpenalty:

-   -   Multiple power sources on-board create a simple path to graceful        degradation, by the sizing of sources so the aircraft is able to        fly on only a subset of these;    -   The ability to design the powertrain with multiple fractional        components, each with high peak-to-continuous performance,        limits the impact of failures to less than an equivalent        fraction of the function. Electric components, e.g., motors,        converters, distribution buses, wiring, switches, allow this        with only modest cost or weight penalties, unlike mechanical or        hydraulic components. Many of these also come with have high        peak to continuous performance capabilities (often heat limited)        so that surviving components can compensate to some degree for        failures in others during recovery periods; and    -   High-speed solid-state sensors and connectors enable detection        and remediation of failures within milliseconds in contrast to        microseconds for traditional contactors or even seconds for        mechanical devices. As a result, embodiments of the inventive        hybrid powertrain are uniquely able to engage redundant        components and redistribute power to surviving components, on a        timescale comparable to the physical.

In some embodiments, a design for graceful degradation includes sizingthe power sources, rechargeable energy storage units and range-extendinggenerators so that the aircraft can maneuver safely in the event of afailure of one or multiple of these elements. For example, the aircraftmay be designed to fly on the rechargeable storage units orrange-extending generators alone, for tolerance to failure in any one.Moreover, a multiplicity of storage units or generators may be used forfurther safety to reduce the likelihood of a complete loss of thesource. This design of power sources is combined with distributionelements (e.g., buses, switches, and wiring) architected to re-routepower in the event of a fault (as illustrated in FIG. 8), so propulsorsreceive equitable distribution from the surviving sources. Thisre-routing is managed by the powertrain optimization and control system(POCS). Failures of the storage units or generators are detected by afault-detection and recovery module of POCS, which then redistributespower optimally to maintain safe flight. In addition, POCS also ensuresstorage units and the fuel system retain sufficient reserves toindependently meet safety requirements.

A design for graceful degradation may also include use of multiplefractional components, propulsors, generators, motors and storage units,for fault tolerance against failure in any one. This may includepowering the powertrain with more than one propulsor or generator, andpowering each with more than one motor, so failure in any one componentdoes not equate to loss of the entire capability. Individual motors maybe designed for peak performance 60-80% above continuous for recoveryperiods of 5-10 minutes, so surviving motors are able to power up tocompensate for motor faults in others. This peak output capability iscombined with distribution (buses, switches, wiring) architected tore-route power to surviving motors to enable them to peak safely.Failures of propulsors, generators, motors or storage units are detectedby the Fault-detection and recovery module of POCS, which thenredistributes power optimally to maintain safe flight.

A design for graceful degradation may also include architecting thedistribution elements (e.g., buses, switches, wiring, fault isolatingcomponents) with redundancy so that the powertrain is resistant tofaults in individual circuits. This may include use of multiple buses,each feeding one or more propulsors, along with back-up buses so thatthe impact of a bus fault is limited to a subset of the propulsors, andso that power to the impacted propulsors can be re-routed via aredundant bus. This bus architecture is combined with wiring andswitches so that power from the sources is distributed equitably toprimary and back-up buses, and so that power to propulsors can be routedvia the primary or back-up bus. This may also include fault tolerantschemes for converters, e.g., redundant converters, or redundant phaselegs, with fault isolation, so functionality of a faulty converter islargely recovered. Failures of the distribution system are detected bythe Fault-detection and recovery module of POCS, which thenredistributes power optimally to maintain safe flight.

A design for graceful degradation may also include design of thepowertrain control system (POCS) so that it is able to operate safely inthe event of a failure of one or more sensors. This may include sensorfault detection capability in the fault-detection and recovery modulewithin POCS, and back-up sensors or sensor-less (sensor independent)monitoring to cover critical sensor failure modes. For instance,propulsor motor fault tolerant control is managed by the fault-detectionand recovery module within POCS that monitors flight conditions todetect and diagnose issues, and then redistributes power to the healthymotors in an optimal way to restore sufficient flight capabilities.

Also included in the inventive design(s) are procedures for safety inthe event of a crash. For example, the fault-detection and recoverymodule within POCS triggers the emergency isolation of high-voltagecircuits, e.g., storage units, generators, convertors, on pilot requestor when significant impact is detected. Note that the gracefuldegradation measures mentioned are coupled with the distributionarchitecture to reroute power with a minimal impact on performance inthe event of a failure. For example, FIG. 8 shows the architecture for arepresentative twin propulsor aircraft with two rechargeable storageunits and a single range-extending generator, implemented using aredundant vital bus.

FIG. 9 is a diagram illustrating an example user interface 900 for useby a pilot of an embodiment of the inventive aircraft. The figure showsvarious operational and status indicators and may be used in anembodiment of an electric-hybrid aircraft that is part of the inventiveair transportation system. In one embodiment, the displays are digitaland represent performance parameters in the same or a similar format tothose of a conventional aircraft for ease of use. The figure illustratesan example of the pilot interface in the “Inflight optimization andcontrol” mode of operation and contains the following indicators andinformation:

-   -   Color coding is chosen to be industry typical to ease pilot        transition. Items in green or white are labels; items in magenta        are active indications of system status. Triangle “bugs” show        either a current indication, or a labeled target indication.        Color coding uses standard green/yellow/red for        normal/caution/danger operating zones;    -   Power indicators (upper left) show the current propulsor power        output both in RPM and % maximum power, as commanded by the        power lever. These are very similar to conventional gas turbine        power output indicators;    -   Speed tape showing current vs. target airspeed (upper right)        utilizes an industry standard vertical airspeed indicator in        units of knots indicated airspeed, KIAS. Specific to this        innovation, shows “speed bugs” at the calculated speeds to fly        for one or more flight modes; in this example, showing “High” at        213 KIAS, “Optimal” at 196 KIAS and ECON is indicated without a        bug to show that it's below the current range of the speed tape;    -   The second row of indicators shows battery, fuel, and power        balance. Battery and fuel are shown with the industry typical        indicators including color coding for normal, caution, and        exhausted energy states. When coupled with an active flight plan        through POCS, an “energy bug” is enabled which shows the        expected energy state on landing (shown on both battery and        fuel). The split pie-chart shows the balance of generation power        to battery power; this is a unique indicator to hybrid-electric        aircraft;    -   The lower quadrants show more detailed data on powertrain        systems and is configured for the current powertrain components.        The example shown here utilizes three discrete packs of        batteries, coupled with a turbo-diesel reciprocating generation        engine; pertinent information for each is displayed using        typical indicator styles. These lower quadrants may display        multiple system information pages, with the pilot able to scroll        through the information. These displays are specific to the        hybrid-electric powertrain implementation; and    -   This cockpit interface to the hybrid-electric powertrain has        multiple modes; in this example mode selection is through a        three position knob on the bottom right. The “flight” mode is        shown here; additional modes could be “Calibration”, invoked        each time a module changes, “Pre-flight” which would initiate        and display status on the internal systems self checks flight,        and “diagnostics” which could display more detailed information        on all systems monitored and controlled, primarily used for        system configuration, maintenance and repair.

In addition to the display shown 900 in the figure and the associatedaircraft functions or systems, the underlying powertrain optimizationand control system (POCS) platform may permit control of one or morespecific powertrain capabilities, including but not limited to therechargeable energy storage units (e.g., batteries, super-capacitors,and range-extending generators), internal combustion engines, or fuelcells. POCS offers a unified interface to the modules of the powertrain,to simplify installation, flight preparation, flight operation anddiagnostics.

The capabilities of POCS are important to the early adoption ofhybrid-electric aircraft, by optimizing operation for maximum efficiencyover regional flights, via quick and safe remediation of faults, byreducing pilot workload and easing pilot transition to electricpowertrain, and by simplifying module changes to alternatives or futuretechnologies. Embodiments of the POCS may assist in the adoption ofhybrid-electric aircraft based regional air transportation systems as aresult of one or more of the following:

-   -   Enables range-optimized regional flights by optimizing sources        of energy over a flight path. To maximize efficiency, energy        sourcing should prioritize the lower cost source, typically the        energy storage units, over the higher cost sources, typically        the generators, over the course of a flight. For instance,        flights over ranges longer than the electric-only range should        deplete the lower cost energy storage units to a minimum        permissible level determined by safety or battery life        considerations. Moreover, sourcing should be charge blended,        utilizing both storage units and generators optimally throughout        the journey, while ensuring energy draw promotes safety and        operating life. POCS enables this by determining an optimal        Energy plan that minimizes the total cost of the flight        (operator defined) within system constraints, based on the        flight path and Flight mode, the departure and arrival Energy        States and characteristics of the aircraft. This defines the        Energy state of the hybrid powertrain along the path to the        destination, e.g., percent state of charge of the battery packs,        percent fuel capacity for the generators, and guides the real        time flow of power from the storage units and generators. POCS        enables further optimization by identifying opportunities to        upsize the energy storage units on low payload flights that are        longer than the electric-only range;    -   Optimally controls the real-time flow of power from the storage        units and generators to achieve the targeted Energy plan.        Although the Energy plan defines an overall sourcing strategy        for the flight, this is inadequate for real-time control given        need to accommodate unpredictable, varying flight environments.        Further, there is need to direct each of the powertrain modules        to deliver the requested power in an optimal way, e.g.,        generator operating on its optimal working curve. POCS enables        this in two stages. First, by determining optimal sourcing for        the power requested that aligns with the Energy plan, defining        real-time power flows from the energy storage units and the        generators. Second, settings of the powertrain modules are        optimized to deliver the requested power with maximized        efficiency, and these are used to direct the module controllers.        For instance, the propulsion power requested is delivered via        optimized settings for the propulsion motors (torque, RPM) and        the propulsor (e.g., fan pitch angle, exhaust plug position).        POCS also manages energy harvesting during the flight, for        instance, via regenerative braking of the propulsors, or via the        generators during low power operations;    -   Enables fault-tolerant control of the powertrain: assists the        operator with preserving normal or gracefully degraded operation        in the event of faults. The hybrid powertrain is designed for        graceful degradation, whereby failure in any area has not more        than a fractional impact on the performance of the powertrain.        This is enabled by multiple power sources onboard, by design        with multiple fractional components, by use of redundant        components and circuitry, and by use of high-speed solid-state        sensors and connectors for quick detection and remediation. POCS        builds on this capability by enabling quick assisted response to        faults for continued safe flight. This is done by continuous        monitoring of the health of the powertrain by the Fault        detection and identification function. A combination of signals        and models are leveraged to identify and isolate faults as        quickly and accurately as possible. If a fault occurs, POCS        alerts the operator to trigger remedial response. POCS may also        trigger a redesign of the Powertrain for graceful accommodation        of the fault, and a redesign of the Controller to adjust to the        potentially redesigned powertrain with fault. The redesign of        the Powertrain and Controls may also be triggered by the        operator. POCS also assists with ensuring safety in event of a        crash, by isolating high-voltage circuits on pilot request, or        when impact is detected;    -   Offers a simplified, unified interface to the hybrid powertrain,        reducing pilot workload and easing pilot transition from        conventional to hybrid aircraft. Key to quick adoption of hybrid        propulsion is ensuring pilots can operate the more complex        powertrain with minimal incremental training POCS enables this        via optimization and controls that shield the pilot from the        added complexity of the powertrain, coupled with an interface        that mimics those of conventional aircraft. In addition, POCS        offers automation to streamline a range of pilot and maintenance        activities, such as powertrain calibration, pre-flight        preparations, inflight control, and powertrain diagnostics; and    -   Streamlines installation of new modules to support forward        compatibility and modularity. This key differentiation of hybrid        powertrain is enabled by POCS in two ways. First, POCS offers        standardized control and monitoring interfaces to a range of        module alternatives, allowing a switchover of generators,        upgrades to advanced technology energy storage units, or the        addition or removal or storage modules to compensate for        payload. Second, POCS enables simple calibration to new modules        via upgrade of aircraft and powertrain models to match, operator        input or from online library, coupled with targeted performance        testing to fine-tune the model to the unit installed. Similar        testing is also performed on a routine basis to ensure models        maintain fidelity as modules age via use.

As will be described with reference to FIG. 10, POCS offers twointerfaces to the operator, “integrated” and “modular”. Integrated is asimplified user interface to the powertrain that mimics the controls ofconventional aircraft, reducing pilot workload and easing transitionfrom conventional to hybrid. Modular is a direct user interface toindividual modules of the powertrain, enabling lower-level fine controlof the operation of the powertrain. These are described in greaterdetail below:

-   -   Integrated. Unified front-end to all POCS capabilities, enabling        the operator to toggle to appropriate operating mode:        Calibration; Pre-flight; Inflight control; Diagnostics. Displays        use performance parameters similar to that used in conventional        aircraft to ease pilot transition to the new technologies and        capabilities. An example of the pilot interface in the “Flight”        mode is shown as display 900 in FIG. 9. The display is coupled        with cockpit controls that are similar to those found in        conventional aircraft today, and which translate operator input        to optimal settings of the underlying hybrid powertrain based on        the defined objective function for the flight, such as:        -   Power levers—one for each propulsor, controlling the power            output of the propulsor. The Power lever angle (PLA)            determines the power output of each propulsor as a percent            of Full power, and enables limited duration surges to Peak            power. The Inflight control module converts power requested            by the Power levers to optimal settings of each propulsor in            real-time, and sources this power optimally from onboard            generators and stored energy units to meet the operator            defined objectives for the flights, within constraints of            the aircraft and powertrain. Some embodiments may also offer            Fan or propeller control levers to control the RPM of each            propulsor, ranging from Maximum to Minimum, with extension            to Feathering. Some embodiments may allow controls of            multiple propulsors to be synchronized, so all coupled            propulsors operate with the same settings, or allow            auto-throttle operation, whereby the Inflight control module            directs the throttle based on the Flight path. In these            situations, a servo motor or similar mechanism is used to            move throttles based on the current power setting (standard            FAA auto-throttle operation).        -   Regenerative braking controls—one for each propulsor,            controlling the regenerating power output of the propulsor.            This is done via dedicated Regenerative braking levers, or            by extending the range of the Power levers to negative power            levels, extending from zero power to full regenerative            power. In both cases, the lever angle determines the            regenerative power output of each propulsor as a percent of            full regenerative power. The Inflight control module            converts regenerative power requested by the levers to            optimal settings of each propulsor in real-time.        -   Reverse power controls—one for each propulsor, controlling            the reverse power output of the propulsor. This may be done            via dedicated Reverse power levers, or by extending the            range of the Power levers to negative power levels,            extending from zero power to full reverse power. In both            cases, the lever angle determines the reverse power output            of each propulsor as a percent of full reverse power. The            Inflight control module converts reverse power requested by            the levers to optimal settings of each propulsor in            real-time.        -   Lower-level controls—offered in some embodiments enable            operators to control the Generators, Storage units and Power            distribution manually. These could include Generator            controls for switching generators on and off, control            generator output from idling to peak power. Controls could            also include a Power distribution control to redirect power            flow from the onboard sources to the propulsor. In a twin            propulsor aircraft with left-right propulsors and left-right            sources, these could offer a choice of Split flows (left to            left, right to right), Directional (Split plus right to left            or left to right) and Coupled (left-right to left-right);            and    -   Modular. Offers a direct interface to individual modules of the        powertrain via their onboard controllers. Intended for        situations where there is need to bypass the flight optimization        capabilities of POCS to engage the controllers directly, e.g.,        repair, emergencies, non-standard operations. The range of        modules that may be accessible for a sample hybrid powertrain is        shown in FIG. 10, and described in greater detail herein.

FIG. 10 is a diagram illustrating the primary functional elements ormodules of a powertrain optimization and control system (POCS) that maybe used in an embodiment of an electric-hybrid aircraft that may be usedas part of the inventive air transportation system. Each or acombination of the functions, operations, or processes performed by orunder the control of the elements or modules shown in the figure may beperformed by the execution of a set of instructions by a properlyprogrammed processing element (such as a controller, state system,microcontroller, CPU, microprocessor, etc.).

As shown in the figure, the elements or functional modules of anembodiment of a POCS platform 1000 may include an “onboard” component1002 and an “online” component 1004. The onboard components, elements,and processes 1002 are typically resident on the aircraft beingcontrolled, while the online components, elements, and processes 1004are typically resident on a data processing platform or system that islocated remotely from the aircraft (such as in a control center,centralized data processing and scheduling platform, etc.) and whichcommunicates with the onboard component 1002 (when necessary) via asuitable communication channel or combination of communication channels(such as a wireless technology coupled to a server that may becommunicated with via the Internet).

In an exemplary embodiment, the POCS platform 1000 functionality isenabled by the following onboard capabilities (components, elements, andprocesses 1002):

-   -   Standard procedures (element/component 1041), which is a library        of preset and operator defined standard operating procedures for        the powertrain and its modules, and may include:        -   Flight mode(s): For instance, Optimal, High speed, Economy,            Custom;        -   Scans and diagnostics: For instance, Initialization scan,            Energy scan, Pre-flight scan, Inflight scan, Post-flight            scan;        -   Operating rules library: Defines operating priorities for            the powertrain, required by safety or based on operator            preference. These constrain the Hybrid energy planner and            Hybrid power manager, and may include:            -   Minimum energy state to ensure adequate safety reserves,                for instance, stored energy units at 20% of capacity,                and generator fuel equivalent to 45 min of flight;            -   Energy state at arrival, for instance, to deplete stored                energy units to minimum levels at 20% of capacity;            -   Power distribution priorities by flight leg. For                instance, taxi on stored energy alone, or approach on                stored energy alone, and with generator on idle for high                availability; and            -   Power level settings by flight leg. For instance, climb                at 80% full power, or for initial descent to be at                neutral thrust.    -   Onboard logs. A database capturing information on key aspects of        the powertrain and its performance. These include: operator        details; onboard modules; operator preferences; lifecycle and        maintenance records; performance logs; checks and diagnostics        logs, access history logs. The database transmits logs to the        Online log (element/component 1023) via the secure datalink        (element/component 1043) periodically, and only stores limited        history onboard.    -   Secure Datalink (element/component 1043). This enables periodic        uploads from Onboard logs to the Online log(s) 1023 for the        specific powertrain, remote diagnostics and maintenance of the        powertrain, and accessing the aircraft and powertrain library        (element/component 1020) for calibration or benchmarking        purposes. The datalink may include 2-levels of security, a lower        level for communicating log or library data, and a higher level        for diagnostics and maintenance data. Access to the datalink is        secure and all access history is logged. This also enables        two-way data flow between POCS and FPOP/FMS for flight data.    -   Module interfaces (element/component 1050). These are connector        interfaces to lower-level controllers of the range of modules        onboard, enabling the controllers to be queried or directed by        the POCS platform, and to transmit a range of state and        performance information to POCS on-demand or continuously.        Typically, API specifications define the protocols by which POCS        and modules communicate. Control modules may include variable        pitch fan controllers, propulsor motor controllers, battery        management systems, engine controllers, fuel system controllers,        generator motor controllers, distribution controllers (switches,        connectors, and convertors), etc.    -   Note that FIG. 12 shows the interface configuration for an        example powertrain 1200 coupled to the POCS onboard by several        interfaces/connectors 1202 for purposes of sensing a performance        parameter and returning a control signal to a component of the        powertrain or its control system. Similarly, FIG. 10 and FIG. 11        show the communications and data flow from the POCS Optimization        Modules 1130 and Powertrain and Controls Manager 1142 to        matching module interfaces (elements 1050 and 1150) of the        powertrain. The system offers the pilot a secondary direct path        (element 1052) to module controllers via the Modular operator        interface (element/component 1012). The system may include        back-up connectors to module controllers for redundancy, along        with connectors and switches to activate the back-up circuitry.

The the POCS platform 1000 may also provide one or more of the followingonline capabilities via a secure POCS cloud-based data platform(element/component 1004):

-   -   Aircraft and powertrain library (element/component 1020). A        library of aircraft and module performance models, including        operating models for each class, and parameters for each module        in a class. The models and parameters are updated periodically        via the benchmarking platform (element/component 1021). The        database in designed to be queried by onboard POCS when        initializing, calibrating a new module, or for periodic        refreshes.    -   Benchmarking platform (element/component 1021). This is a        database of performance benchmarks, and may include input        capability for external benchmarks, and upload of raw        performance data from the online logs for individual        powertrains. Also includes statistical or other data analysis        procedures that update benchmarks periodically.    -   Diagnostics platform (element/component 1022). This has the        capability of enabling remote diagnostics and maintenance of the        powertrain over a highly secure datalink.    -   Powertrain logs (element/component 1023). This serves as an        archive of Onboard logs from individual powertrains uploaded        periodically via the secure datalink, coupled with comparative        performance statistics drawn from the Benchmarking platform.

In a typical embodiment, an implementation of a POCS platform (such aselement 1000 of FIG. 10) may offer the following functionality orcapabilities:

-   -   Calibration (represented by element/component 1025). This        tailors the optimization and control platform to accommodate        specific modules onboard, enabling upgrades to future        technologies, aircraft variants, up/downsizing energy storage        units or generators, and high fidelity modeling of module        performance. In some embodiments it may perform or assist in        performing the following functions/operations:        -   Scan powertrain to identify changes to modules onboard            relative to most recent scan, validate and record in Onboard            log;        -   Download optimization and control parameters for all changed            modules from the Online Aircraft and Powertrain library via            the datalink and populate onboard models;        -   Calibrate models to performance of onboard modules. Step            operator through a series of tests on the modules, defined            by the Initialization scan procedure to assess actual versus            model performance. Identify potential issues and alert.            Adjust model parameters to better match actual performance;            and        -   Enable operator to define range of preferences around            powertrain optimization and control, displays, reporting,            monitoring and diagnostics. Includes setting tailored to the            specific operating environment, mission profiles and            trade-offs. Store preferences in Onboard log.    -   Flight prep (represented by element/component 1026). This        performs automated checks to ensure the powertrain has adequate        energy to safely complete the planned flight, and is in flight        ready state. In some embodiments it may perform or assist in        performing the following functions/operations:        -   Accept Flight mode or Optimal as default, and flight            details: Air path or Flight time (or distance), Payload and            an Uncertainty factor. These can be entered manually or via            FPOP;        -   Calculate and display Energy state based on Energy state            scan procedure;        -   Determine if additional generator fuel or stored energy is            required by using the Hybrid Energy Planner with prescribed            flight details, Flight mode and Energy state. Examine            Payload versus design payload to ensure safe flight, and to            assess if there is option to increase capacity of stored            energy units;        -   If onboard energy or Payload is changed, via additional            stored energy units, increased state of charge or fuel,            re-run Hybrid Energy Planner; and        -   Execute pre-flight tests on the powertrain defined by            Operating procedures, and identify issues, trigger the Fault            detection and recovery module.    -   Inflight Control (represented by element/component 1027). This        enables simplified control of power delivered by the hybrid        powertrain, optimizing powertrain and module performance based        on operator selected Flight mode and flight details. Control may        be semi- or fully-automated, and optimization may be Basic or        Integrated. In some embodiments it may perform or assist in        performing the following functions/operations:        -   Calculate the optimal Energy plan, Arrival energy state,            Target speeds and ranges (Maximum, Optimal, and Economy)            using the Hybrid energy planner based on flight details,            Flight mode and Energy state Flight details are either            Basic, with Flight time (or distance) as input, or            Integrated, with Air path as input. Display Arrival energy            state and Target speeds. The Energy plan describes the            Energy state along the Air path: Stored energy and Generator            fuel at discrete waypoints;        -   If Arrival energy state is below minimum reserve levels,            alert the operator, and offer alternate Flight mode, Target            speed settings to make the destination;        -   Control the powertrain in real-time to achieve the Energy            plan, in tandem with operator input, optimally sourcing            power from the storage unit and generators, making            adjustments as conditions change. FIG. 11 provides an            overview of the Inflight control process and the functional            modules or sub-processes that may be utilized, and is            described in greater detail herein. This control process may            include the following functions or operations:            -   Determine real-time control strategy using the Hybrid                power manager, defining optimal energy distribution                across the generators and stored energy units;            -   Pass the energy distribution to the module optimizers                which compute optimal settings for the powertrain                modules, and transmit these to the lower-level module                controllers via Module interfaces within POCS;            -   Refresh Energy plan periodically based on deviation from                prior plan;            -   Refresh Energy state periodically via the Energy state                scan procedure; and            -   Enable updates to Flight mode and flight details                manually or via FPOP (described with reference to FIG.                14), and respond by refreshing the Energy plan.        -   Enable semi-automated or fully-automated operation: the            operator controls the Power levers in the former; the            Inflight control module directs all functions in the latter,            adjusting requested power levels to deliver the optimal            airspeed; and        -   Continuously monitor the performance of the powertrain via            the module optimizers, and assess against models, safe            limits via Inflight scan procedure. In event of issue,            trigger the Fault detection and recovery module to            coordinate alerts and action.    -   Diagnostics (represented by element/component 1028). This        performs post-flight mission analysis, powertrain diagnostics        and issue resolution. In some embodiments it may perform or        assist in performing the following functions/operations:        -   Run the Mission analysis algorithm on monitored data stored            in the Onboard log to calculate and display key flight            statistics (e.g., distance, time, average speed), detail on            total energy used, fuel and stored energy remaining, key            performance statistics (e.g., overall efficiency and by            module). Store results in Onboard log;        -   Update operating history of modules or components that            require periodic maintenance or are life-limited; and        -   Monitor health and performance of the powertrain, and assess            against models, safe limits via Post-flight scan procedure.            In event of issue trigger the Fault detection and recovery            module to coordinate alerts and action.    -   Fault detection and Recovery (represented by element/component        1042). This performs ongoing monitoring of the powertrain to        detect and identify faults, alert the operator, and assist with        recovery action. In some embodiments it may perform or assist in        performing the following functions/operations:        -   Monitor the health of the powertrain by the Fault detection            and identification function, leveraging a combination of            signals and models to identify and isolate faults as quickly            and accurately as possible;        -   If a fault occurs, alert the pilot to trigger remedial            response via the Powertrain alert function;        -   If a fault occurs, determine action required and trigger the            Powertrain and Controls manager to execute in concert with            the pilot; and        -   Remedial action may also be initiated by the pilot engaging            the Powertrain and Controls manager to execute.

In some embodiments, the POCS determines an optimal Power plan based onflight details and a prescribed Flight mode. POCS then controls theoperation of the powertrain and its modules during flight to match thePower plan by monitoring performance of the powertrain and modules,making adjustments when necessary. POCS is designed for semi-automatedor fully-automated operation, with the pilot retaining control of thethrottle in the former, while POCS controls all functions in the latter.However, the pilot is able to override POCS settings.

FIG. 11 is a diagram illustrating the primary functional elements ormodules of a POCS that may be accessed and used to control or modifyon-aircraft processes in an embodiment of the inventive airtransportation system. Each or a combination of the functions,operations, or processes performed by or under the control of theelements or modules shown in the figure may be performed by theexecution of a set of instructions by a properly programmed processingelement (such as a controller, state system, microcontroller, CPU,microprocessor, etc.).

As shown in the figure, the elements or functional modules of theon-aircraft processes of an embodiment of a POCS 1100 may include:

Optimization Modules (Element 1030 of FIG. 10 and/or Element 1130 ofFIG. 11)

-   -   Hybrid energy planner (element 1132 of FIG. 11):    -   Determines the optimal Energy path over an Air/flight path by        minimizing a non-linear cost objective (see below) subject to        initial and arrival Energy states, Module performance        constraints and Operating rules, typically a charge blended        strategy that looks to gradually deplete the stored energy units        over the course of the flight, enabling each of the power        sources onboard to operate with optimal efficiency;    -   Performed by decomposing the trip into an Air path, composed of        segments with roughly uniform operating requirements, e.g.,        taxi, take-off roll, climb at uniform rate, cruise, power        neutral descent (done as part of Flight prep). Optimization is        then performed to determine the optimal Energy plan along the        provided Air path. If a detailed Air path is not provided, a        standard depletion profile is assumed, for instance, linear over        the cruise and climb legs, after budgeting for taxi, take-off,        descent and landing based on a look-up table of benchmarks;    -   Optimization is performed via full dynamic programming (or a        similar algorithm), or simplified approaches such as using        look-up tables or functions to determine optimal power        distribution across the generators and the stored energy units        based on the flight leg and operating conditions. Power        distribution could be described in one of many ways, including        the Generator power setting, as fraction of full generator        power, or the Power ratio, equal to the ratio of power drawn        from stored energy to the total power requested;    -   The objective function defines the quantity to the minimized        over the course of the Air path by the Hybrid energy planner.        For example, the objective function may include one or several        of the terms below, with parameters defined by the operator:        Objective function=Cost of fuel+Cost of stored energy+Cost of        engine maintenance and reserves (amortized)+Cost of battery        packs (amortized)+Cost of passenger and crew time+Cost of        aircraft+Cost of emissions; and    -   The objective function is minimized based on provided departure        and arrival Energy states, Operating rules from the Operating        rules library, powertrain and module performance constraints        from the powertrain and module (propulsor, generator, stored        energy) models. The optimization process requires simulation of        aircraft and powertrain performance, provided by the Aircraft        and Powertrain performance models.    -   Hybrid power manager (element 1134 of FIG. 11):    -   Determines real-time control strategy to optimize energy        distribution, described via variables such as the Generator        power setting or Power ratio, across onboard sources to deliver        the power demanded, based on the overall Energy path for the        flight. This is determined by minimizing a non-linear objective        for the flight segment subject to Module performance constraints        and Operating rules, including the provided Energy path;    -   Optimization may be performed by a relatively simple method,        such as determining the Generator power setting (or Power ratio)        from a look-up table of optimal values by flight leg and        discrete range of operating conditions, or by a more complicated        method, such as determining the optimal value using one of        several algorithms such as Pontryagin's minimum principle (PMP)        or the Equivalent consumption minimization strategy (ECMS).        Alignment with the provided Energy plan is driven by an outer        control loop, e.g., proportional plus integral;    -   The objective function defines the quantity to the minimized        over the course of the Air path by the Hybrid energy planner.        For example, the objective function may include one or several        of the terms below, with parameters defined by the operator:        Objective function=Cost of fuel+Cost of stored energy+Cost of        engine maintenance and reserves (amortized)+Cost of battery        packs (amortized)+Cost of passenger and crew time+Cost of        aircraft+Cost of emissions; and    -   The objective function is minimized based on provided departure        and arrival Energy states, Operating rules from the Operating        rules library, powertrain and module performance constraints        from the powertrain and module (propulsor, generator, stored        energy) models. The optimization process requires simulation of        aircraft and powertrain performance, provided by the Aircraft        and Powertrain performance models.    -   Propulsor optimizer (element 1136 of FIG. 11):    -   Determines real-time control strategy for each of the propulsors        based on power requested, airspeed and environmental conditions.        Translates power requested to propulsor settings for optimal        efficiency. The optimal settings are then used to direct the        lower-level module controllers (e.g., variable pitch fan        controller, motor controller) via Module Interfaces (elements        1050 of FIG. 10 and/or elements 1150 of FIG. 11) within the POCS        platform. The optimal settings may be further modified via a        fine control loop for improved performance. This may include a        peak seeking loop to fine-tune the operating point, and a        smoothing loop to moderate abrupt changes in settings over        intervals determined by ride comfort, aircraft structural or        powertrain performance constraints;    -   Settings optimized may include the attitude of the propulsors,        e.g., variable pitch fan angles, position of the exhaust plugs,        and the output of the propulsor motor-inverters, e.g., torque,        speed. The optimizer regulates propulsor setting over the range        of aircraft operations including standard thrust, neutral        thrust, regenerative braking, reverse thrust and recovery        thrust;    -   For standard thrust control, the optimizer is driven by        requested power for each propulsor, airspeed and environmental        conditions, and determines propulsor settings that maximize the        thrust delivered. This is done by performing a staged or coupled        optimization across the Motor and the Propulsor performance        models (element 1040 of FIG. 10 and/or element 1140 of FIG. 11).        In the staged approach, motor and propulsor settings are        optimized in turn. For instance, motor settings to maximize        efficiency may be determined first, by optimization using the        Motor performance model within operating constraints defined for        the motor. Following this, the propulsor attitude is determined,        e.g., fan pitch angle or position of exhaust plug, to maximize        propulsor thrust by optimization using the Propulsor performance        model within operating constraints defined for propulsor        attitude. These settings are then used to direct the operation        of the lower level controllers via the Module Interfaces within        POCS;    -   In some implementations, a look-up table may be used to        determine near-optimal values, followed by an optional        optimization step to refine estimates along the lines of those        described above;    -   For reverse thrust, the optimizer is driven by requested reverse        power for each propulsor, and determines propulsor settings that        maximize the reverse thrust delivered. This is done by process        similar to that for standard thrust. In the case of a staged        approach, the motor settings are determined to maximize        efficiency, by optimization using the Motor performance model,        or by look-up in the Motor performance table. Then the matching        propulsor attitude is determined by optimization using the        Propulsor performance model or by look-up in the Propulsor        performance table;    -   For regenerative braking thrust control, the optimizer is driven        by requested reverse power for each propulsor, airspeed and        environmental conditions, and determines propulsor settings that        maximize the thrust delivered. This is done by performing a        staged or coupled optimization across the Motor and the        Propulsor performance models. In the staged approach, motor and        propulsor settings are optimized in turn. For instance, motor        settings to maximize efficiency may be determined first, by        optimization using the Motor performance model within operating        constraints defined for the motor. Following this, the propulsor        attitude is determined, e.g., fan pitch angle or position of        exhaust plug, to maximize propulsor reverse thrust by        optimization using the Propulsor performance model within        operating constraints defined for propulsor attitude. These        settings are then used to direct the operation of the lower        level controllers via the Module Interfaces within POCS; and    -   For neutral thrust, the optimizer directs the lower-level        controllers to cut off power to the motors, and set the        propulsor attitude to minimal drag, e.g., variable pitch fans        set to feathering or pin-wheeling, exhaust plug set to maximum        extension.    -   Stored energy optimizer (element 1138 of FIG. 11):    -   Monitors performance and state of the rechargeable storage units        via the Module Interfaces 1150 within POCS, to help ensure        operation within long life ranges defined by performance        constraints. If the storage units are outside of their long life        ranges, the optimizer adjusts the hybrid energy planner and        hybrid power manager settings to redistribute power to the        generators, e.g., by increasing the effective cost of the        storage units;    -   Generator optimizer (element 1140 of FIG. 11):    -   Determines real-time control strategy for each of the generators        based on power requested, airspeed and environmental conditions.        Translates power requested to generator settings for optimal        efficiency. The optimal settings are then used to direct the        lower-level module controllers (e.g., engine control unit, motor        controller, fuel system controller) via Module Interfaces 1150        within the POCS platform. The optimal settings may be further        modified via a fine control loop for improved performance. This        may include a peak seeking loop to fine-tune the operating        point, and a smoothing loop to moderate abrupt changes in        settings over intervals determined by ride comfort, aircraft        structural or powertrain performance constraints;    -   Settings optimized may include the output of the internal        combustion engines, e.g., speed, torque, and the draw of the        generator motor-inverters, e.g., torque, speed;    -   The optimizer is driven by requested power for each generator,        airspeed and environmental conditions, and determines generator        settings that maximize efficiency. This is done by performing a        staged or coupled optimization across the Engine and Motor        performance models (or the integrated Generator model). In the        staged approach, engine and motor settings are optimized in        turn. For instance, engine settings to maximize efficiency may        be determined first, by optimization using the Engine        performance model within operating constraints defined for the        engines. Following this, the motor settings to maximize        efficiency are determined by optimization using the Motor        performance model within operating constraints defined for the        motors. These settings are then used to direct the operation of        the lower level controllers via the Module Interfaces within        POCS;    -   In some implementations, a look-up table may be used to        determine near-optimal values, followed by an optional        optimization step to refine estimates along the lines of those        described above; and    -   Includes strategy to route excess power (above that requested)        from the generators to charge the storage units to insulate        generators from transients, or when power requested is outside        of generator optimal range.    -   Powertrain and Controls manager (element 1142 of FIG. 11):    -   Driven by input from the pilot or the Powertrain and Controls        redesign function, executes diagnostics or resolution processes,        reconfigures the powertrain or changes the control laws;    -   Receives resolution or diagnostic process steps, powertrain        reconfiguration instructions, control laws from the pilot and        the Powertrain and Controls redesign function;    -   Resolves conflicting commands and follows safety procedures        defined in the operating rules function;    -   Executes the rationalized set of changes in a safe sequence by        directing the lower-level controllers via Module interfaces, and        by modifying the optimization modules, aircraft and powertrain        models; and    -   For instance, in event of an impending emergency landing, a        “secure and isolate” sequence triggered by the pilot immediately        before touchdown would direct the Powertrain and Controls        redesign function to shut down or isolate all high-voltage or        flammable systems of the powertrain to protect passengers and        cargo. Alternately, the Fault detection and identification        function may trigger the sequence based on assessment of a crash        from the aircraft state variables.    -   Power allocator (element 1144 of FIG. 11):    -   Determines power distribution across on-board propulsors based        on pilot direction and powertrain capabilities. This may        include:        -   Power allocation to coordinate multiple propulsors, for            instance balanced power to eliminate yaw moment, e.g.,            propulsors powered for zero moment about the aircraft center            of gravity, or propulsor power determined by power setting            of a master propulsor;        -   Power allocation to accommodate propulsor faults optimally,            preserving normal or gracefully degraded performance aligned            with requested power. For instance, allocation may boost            power to healthy propulsors to compensate for faults, while            limiting yaw moment, ensuring power is above minimum needed            to maintain safe flight for that flight leg, and does not            exceed constraints on the propulsors; and        -   Power allocation for directional control, by distributing            power to create a requested yaw moment.

Aircraft and Powertrain Models (Element 1040 of FIG. 10 and/or Element1150 of FIG. 11)

-   -   Aircraft performance model (element 1152 of FIG. 11):    -   a flight test calibrated, single degree of freedom, physics        based performance simulation model which calculates the expected        power required for the current phase of flight given the        aircraft weight, velocity, air temperature, and pressure, and        rate of climb or descent (a further description of this aspect        is found in the discussion of the FPOP system).    -   Powertrain and Propulsor model(s) (elements 1153 and 1154 of        FIG. 11):    -   Performance models, look-up tables and performance constraints        that enable optimization of propulsor settings based on power        requested, airspeed and environmental conditions. These may        include one or more of the following:        -   Motor performance model, for instance, describing the            efficiency of the motor as a function of motor torque, speed            and voltage;        -   Propulsor performance model, for instance, defining            propulsor thrust as a function of the fan pitch angle,            torque, airspeed, fan speed, and setting, standard, reverse            or regenerative braking;        -   Motor and propulsor performance look-up tables defining            performance relationship at discrete points, as replacement            for optimization, or for use to generate starting            approximations; and        -   Performance constraints on motor and propulsor settings. For            instance, fan pitch angle ranges for standard operation,            regenerative braking and reverse thrust.    -   Generator model (element 1156 of FIG. 11):    -   Performance models, look-up tables and performance constraints        that enable optimization of generator settings based on the        power requested, airspeed and environmental conditions. These        may Include one or more of the following:        -   Engine performance model, for instance, defining engine            efficiency as a function of the engine torque, speed, and            ambient conditions;        -   Motor performance model, for instance, describing the            efficiency of the motor as a function of motor torque, speed            and voltage;        -   Engine and motor performance look-up tables defining            performance relationships at discrete points, as replacement            for a performance model, or for use as starting            approximations;        -   Alternately, a generator motor for integrated engine-motor            performance, for instance, describing generator efficiency            as a function of torque, speed, voltage and ambient            conditions. Similar to above, the generator motor could be            replaced by or supplemented with generator performance            look-up tables defining performance relationships at            discrete points; and        -   Performance constraints on engine and motor, or integrated            generator settings. For instance, engine power ranges to            full power, boost and peak, motor power ranges to full            power, boost and peak, along with safe durations for boost            and peak.    -   Stored energy model (element 1158 of FIG. 11):    -   Performance models, look-up tables and performance constraints        to enable optimization of power distribution across the        rechargeable stored energy units and generators, based on power        requested, current state of charge, environmental conditions.        These may include the following:        -   Drawdown model for the stored energy units, which relates            the state of charge of the units to the current drawn, for            example, via generic Coulomb counting;        -   Stored energy performance model, that determines operating            efficiency of the units based on the power drawn, state of            charge, ambient conditions, and other factors. For instance,            a Rint type equivalent circuit model coupled with models for            key parameters, such as for the open circuit voltage as a            function of the state of charge and temperature;        -   Stored energy performance look-up tables defining            performance relationship at discrete points, as replacement            for optimization, or for use as starting approximations; and        -   Performance constraints on stored energy units, including            limits on the state of charge and power drawn from the            units.

Fault Detection and Recovery (Element 1042 of FIG. 10 and/or Element1160 of FIG. 11)

-   -   Fault detection and identification (element 1162 of FIG. 11):    -   Continually monitor the health of the powertrain by combination        of signal-based and model-based methods to detect sensor,        actuator, component or module faults;    -   Periodically sample signals from a range of sources, control        signals from POCS to the lower-level controllers, output signals        from the lower-level controllers, powertrain and module sensors,        aircraft state variables;    -   Monitor signals to ensure powertrain is operating within safe        limits defined by performance constraints. If safe limits are        exceeded, monitor the extent and duration of the spike to assess        severity of the issue;    -   Trigger powertrain alerts (element 1164 of FIG. 11) to notify        the pilot, via the in-cockpit interface (element 1170, and more        specifically, Pilot Alerts element 1172);    -   Leverage a variety of methods to detect faulty signals, e.g.,        Fourier analysis, limit checking;    -   Compare the performance of the powertrain, modules and        sub-systems with internal models for components or processes to        identify potential faults, via methods such as parameter        estimation or neural networks;    -   Determine the location and nature of the fault, via signals and        models using analytic and/or heuristic methods. Classify faults        based on location, type and severity; and    -   Trigger the Powertrain and Controls Redesign function/process        (element 1166 of FIG. 11) to initiate corrective action.        Note that for purposes of management of the aircraft and        transportation system, a powertrain configuration and control        law library may include the following information, data, or        processes:    -   A resolution process that describes the process steps to be        followed to resolve a fault with the powertrain;    -   Each powertrain configuration describes settings, e.g.,        switches, connectors, contactors, that collectively need to be        set to implement the architecture, along with process steps to        execute a safe reconfiguration, and the control law to operate        the reconfigured powertrain; and    -   Each control law describes optimization and control procedures        for the powertrain, including objective functions, operating        rules, powertrain and module performance constraints, and        aircraft and powertrain performance models.    -   Powertrain and Controls Redesign (element 1166 of FIG. 11):    -   Determine powertrain and controls redesign required to        accommodate active faults such that normal or gracefully        degraded performance is preserved, by combining pre-defined        designs with in-flight synthesis;    -   Determine if corrective action is required based on location,        type and severity of faults;    -   Select resolution processes, powertrain configurations and        control laws to optimally accommodate a fault via an expert        system (or other decision process) that combines look-up within        libraries of pre-defined resolution processes, powertrain        configurations and control laws, with synthesis to tailor a        response to the specific condition. For example:        -   Isolation of faulty modules or circuits. For instance, in            the case of a short-switch fault in a converter, a            fast-acting fuse connected to the switch can be used:            clearing the fuse isolates the switch when faulted;        -   Redistribution of power to accommodate faults. For instance,            in a powertrain with twin propulsors, left and right, each            powered by a stored energy unit and generator, faults in a            propulsor or source may require allowing left-right            transfers to optimize output. A left to right transfer would            help compensate for faults in the left propulsor, by            allowing the right to be boosted. Similarly, a left to right            transfer would help accommodate faults in the right power            sources, so both can be powered equally;        -   Activation of redundant modules or circuits. For instance,            in the powertrain with twin propulsors, left and right, each            powered by a bus, failures in either of the buses can be            accommodated by a single redundant bus. Moreover, the            redundant bus can also be used to create a path for            left-right transfers; and        -   Isolation of high voltage circuits.    -   Initiate alerts and corrective action by triggering the        Powertrain Alerts (element 1164 of FIG. 11) and Powertrain and        Controls Manager (element 1142 of FIG. 11) functions,        operations, or processes.

FIG. 14 is a flowchart or flow diagram illustrating certain of theinputs, functions, and outputs of a Flight Path Optimization Platform(the FPOP) that may be used to determine or revise a flight path for anelectric-hybrid aircraft that may be used as part of the inventive airtransportation system. Each or a combination of the functions,operations, or processes performed by or under the control of theelements or modules shown in the figure may be performed by theexecution of a set of instructions by a properly programmed processingelement (such as a controller, state system, microcontroller, CPU,microprocessor, etc.).

An implementation of the Flight Path Optimization Platform may be usedto determine the optimal flight path(s) for a hybrid-electric aircraft.This includes defining speeds and altitudes, and an Energy plan for eachof a series of flight segments while satisfying the performance and costobjectives defined by the Flight Mode. The FPOP determines optimal pathsacross one or multiple flight tracks; in doing so, it takes into accountaircraft and powertrain characteristics, weather conditions, ATCrestrictions, hazards, etc.

Note that flight planning for a regional hybrid-electric aircraft withmultiple power sources requires a more complex set of trade-offs than aconventional aircraft being piloted over long ranges. For instance, fora hybrid-electric aircraft the optimal flight altitude is determined bya combination of speed versus efficiency objective, flight distance,weather aloft, aircraft aerodynamics, available energy and power, andrelative stored energy versus generator usage. In contrast, thedesignated flight altitude for a long distance commercial passenger orcargo flight may be set by one or more of FAA requirements, governmentpolicies, and coarse aircraft characteristics. This is a much simplermanner of determining a segment (or segments) of a conventional longrange flight. Because of the complexity of the flight planning processrequired for the inventive aircraft and regional air transportationsystem, the FPOP is used to execute the required optimization processesboth pre-flight and during flight (as conditions change) to determine anoptimal flight path.

In addition to primary flight path planning, FPOP may also be utilizedon a periodic basis in flight to update the flight path to thedestination (given changes in winds, ATC routing etc.), and providealternate destinations or flight paths in case of failures within thepowertrain, or other inflight emergencies:

-   -   During flight, periodically identifies all airports within range        of the aircraft given current energy state. Results may be        displayed to the pilot in any manner of formats including a        range ring on a map, an airport highlight on a map, a simple        text list etc.;    -   In case of any emergency situation, immediately provides the        flight path to the nearest acceptable alternate airport; and    -   In case of a partial failure in the powertrain, FPOP will        identify alternate destinations available with the degraded        condition of the powertrain. Examples of partial failures would        include failure one or more energy storage units, generation        modules, propulsion motors etc.

In some embodiments or implementations of the FPOP platform or dataprocessing system, an optimization process may be performed on twolevels:

-   -   Level 1: A simple rule-based calculation using standard        libraries to set altitudes and speeds based on Flight mode and        distance; and    -   Level 2: Optimization across a range of viable altitude and        speed alternatives, building on Level 1 output.

In some embodiments, the FPOP platform may include or be configured toaccess one or more of the following functions, operations, or processes:

-   -   Path generation (element or process 1404 in FIG. 14). This        defines the Level 1 Flight path for each Flight track. This        module Constructs a 3D Flight path, defined by waypoints        (latitude, longitude, and altitude) connected by flight segments        (for example, cruise, climb, descent), with a speed and Energy        plan assigned to each segment. Cruise may consist of one or more        segments as required by altitude constraints and ATC routing. In        the case of Level 2 optimization, builds alternate Flight paths        for each track using the Path alternatives generation rules        module (1413). For each Flight path, determines target speeds by        leg using the Speed rules library, and determines the Weather        and Caution indexes by interpolating across provided conditions.        In general, the path generation process or element utilizes a        core sequence which draws from libraries of performance        heuristics and airspace constraints, such as the following:        -   Path generation sequence first sets cruise altitude(s) and            flight speeds from heuristics. Climb and descent distances            are calculated to set intermediate waypoints, airspace            constraints are calculated as waypoints with altitude            constraints. Lastly, Power ratio (range extending generator            state) is set for each segment;        -   Path heuristics (element 1407 in FIG. 14) A library of            altitudes, speeds and energy source utilization based on a            database from extensive flight path optimization. For a            given range, weight and Flight mode, returns the optimal            climb and descent rates, cruise altitudes and speeds, and            range extending generator utilization times for a no-wind,            simple flight profile. Heuristics may be generated using the            process described herein;        -   Airspace constraints. (element 1410 in FIG. 14) Utilizes the            navigation database of airspace and terrain, combined with            the flight track, to determine minimum or maximum altitude            constraints, imposes the constraints along the Flight track            as start and end (latitude, longitude, and altitude)            waypoints;        -   Climb, descent library. (element 1409 in FIG. 14) A library            which returns time and distance to climb or descend between            two altitudes at the current weight, and speed provided by            the Path heuristics. Library may contain table look-ups with            interpolative smoothing, or compiled performance            calculations;    -   Environment Evaluation. (element or process 1412 in FIG. 14)        Determines whether environmental conditions warrant a level of        path optimization beyond the baseline heuristic path. Applies        weather and cautions data to the route of flight; any cautions,        significant wind, or significant changes in wind on the flight        path will require the L2 Path refinement.    -   Alternate flight paths generator (element or process 1413 in        FIG. 14). Builds a set of alternate Flight paths by altering        segment altitudes from the initial Flight path. Uses the        Breakpoint generator to further divide existing flight segments        with additional waypoints if warranted, and then generates the        set of all possible paths. The maximum number of paths        (order 10) is limited by altitude constraints (minimum,        maximum), and airspace rules which require cruise at incremental        altitudes (eg: over the US, eastbound flights cruise at        odd-thousand feet, 9000, 13000 etc.);    -   Break point generator (element or process 1414 in FIG. 14). This        routine compares the existing cruise segments against the        Cautions and Weather index data (elements 1403 and 1405).        Typically, waypoints are inserted at the boundaries of any        caution, and are also inserted at any location with significant        wind velocity change. Each additional waypoint increases the        degrees of freedom available to the optimizer;    -   Flight path optimizer (element or process 1408 in FIG. 14). This        varies the cruise speed(s) and Power ratio over a Flight path to        minimize an objective function while meeting constraints.        Optimization is performed for the current aircraft state, which        may include weight, stored energy, and range extending generator        fuel available, and environmental conditions which may include        winds, precipitation, temperatures etc. Results of the        optimization process may include the optimized Flight path, Air        path, Energy plan, and value of the objective function. The        flight path optimizer may include one or more of the following        processes, operations, functions, elements, etc.:        -   Objective function. Set by Flight mode, the Objective            function will affect the cruise speed and energy utilization            strategy. Example objective functions which “bracket” the            performance space would typically be maximum speed (minimum            time), or minimum energy. A more comprehensive objective            function may include one or several of the terms below, with            parameters defined by the operator: Objective function=Cost            of fuel+Cost of stored energy+Cost of engine maintenance and            reserves (amortized)+Cost of battery packs (amortized)+Cost            of passenger and crew time+Cost of aircraft+Cost of            emissions;        -   Optimization variables. Optimizer varies cruise speed(s) and            Power ratio. For example, a maximum speed optimization would            result in a high level of range extending generator usage,            while a minimum energy optimization would result in a level            of range extending generator usage dependent on flight            range, sufficiently short flights would not use range            extending generators at all;        -   Optimization constraints. May include one or several            constraints on the powertrain for performance and safety            including maximum discharge rate of stored energy, minimum            state of charge at any point during the flight, minimum            energy reserves at end of flight (note that optimization            occurs on a fixed Flight path; any altitude constraints have            been satisfied by the Flight path generator);        -   Optimization process. The optimization space is nonlinear            and may contain discontinuities with power generator state,            both of which preclude a closed-form solution. Optimization            requires modelling the aircraft and powertrain performance            over the defined Flight path in a time dependent manner,            using the current aircraft configuration and in the expected            flight environment. Performance models result in time            integrated totals which are used to calculate the objective            function (for example: fuel and stored energy consumed);        -   Flight modelling may be accomplished with dynamic            programming, for example a flight simulation including            representative aircraft and powertrain models (described in            greater detail below), or by simplified methods, such as            reduced order models (so long as discontinuous, time            integrated properties are correctly modelled). The method            described herein utilizes a flight simulator process with            representative aircraft and powertrain models, and            incorporates the impact of the current operating            environment;        -   Optimization algorithms. A flight profile, with a single            cruise speed variable may be optimized with a gradient            descent, or Newton's method. A multi-segment flight with            discontinuities in Power ratio may require more advanced            nonlinear algorithms, such as NPSOL;    -   Constraints Check (element or process 1406 of FIG. 14) checks        the results of the optimized flight path against required end of        flight energy reserves or other constraints which may be used to        shape the optimization space. Any path which could not be        optimized to meet constraints is discarded at this point as        non-viable;    -   Path evaluation (element or process 1402 of FIG. 14). This sorts        all valid Flight paths by objective function, returns the        default Flight path (as initially requested), and the optimized        (i.e., that having the minimum objective function) Flight path        with all relevant information;    -   Flight simulation models and modules. The flight simulation        model may be utilized by the Flight path optimizer (element or        process 1408 of FIG. 14) and is a flight test calibrated, single        degree of freedom, physics based performance simulation model        which calculates the expected power required for the current        phase of flight given the aircraft weight, velocity, air        temperature, and pressure, and rate of climb or descent. The        model utilizes Aircraft and Powertrain models in time stepping        and empirical routines to continuously calculate performance        along the Flight path in the presence of forecast weather. The        results are integrated totals for time, distance, and energy.        The integrated distance totals are the Air path. These models        may include one or more of the following:        -   Flight modules. Performance is calculated for each flight            segment by the corresponding flight module (e.g., takeoff,            climb, cruise, descent, landing, etc.). The modules are            initiated with aircraft and segment information, and return            the integrated performance for the complete flight segment.            A Table provides the details on inputs and outputs for each            module, where the modules utilize the Aircraft and            Powertrain models to calculate aircraft performance;        -   Aircraft model. The model may be initiated with the aircraft            state (altitude, velocity, power level, weight, turn rate            etc.), and operating environment (altitude, air temperature,            pressure, density) and returns the corresponding            instantaneous performance (energy usage, fuel burn,            acceleration, climb or descent rate etc.). The model may            utilize a combination of force and moment equations (C_(L),            C_(D), C_(Di), C_(M), F, and N_(Z)W), and comprehensive            table look-ups to determine instantaneous aircraft            performance, where:            -   C_(L)—Standard calculation of C_(L)=N_(Z)W/q/S;            -   C_(D)—Drag build-up through a Reynolds based skin                friction methodology with form drag factors, corrected                to test drag. Additional factors for cooling drag, flap                and landing gear drags (if needed), excrescence and                interference drags;            -   C_(Di)—Induced drag with baseline C_(L) ²/(π AR e), e                provided by table look-up, function of C_(L), flap                setting. Trim drag added as lift increment to main wing,                and C_(Di) from the HT;            -   C_(M)—Pitching moment, from aircraft weight, CG, and                neutral point (speed dependent, from table look-up);            -   F—Thrust, both available and required. Powertrain and                propulsor models called to determine SHP available,                converted to thrust with aerodynamic propulsor model                (table look-up of efficiency Vs. Speed). Thrust required                calculated to balance drag (in case of non-maximum                thrust), and used for energy/fuel burn; and            -   N_(Z)W—Load factor, expressed in fractions of (g), due                to accelerated flight (turning, or pitch rate);        -   Powertrain model. Represents the physics of hybrid-electric            powertrain modules and propulsors. In response to a thrust            requirement from the aircraft, powertrain module distributes            power between range extending generators and energy storage            units, returns thrust available, range extending generator            state(s), fuel burn rate, and storage discharge rate. The            aircraft simulation tracks range extending generator run            time, total fuel burned, and kWh of storage used. Additional            information on the powertrain models is provided in the            powertrain section (e.g., elements 1153 and 1154 of FIG.            11).

As noted, the FPOP flowchart or flow control diagram shows the sequenceof steps in an exemplary implementation of the FPOP process. Thesetypically include:

1. The FPOP is initialized from the POCS (1409); data needed for theflight path generation/optimization may be gathered from severalsources:

-   -   a. Pilot input Flight mode information (1410) is provided by the        POCS, which also includes energy state requirements (e.g., level        of reserve needed on landing)    -   b. The GPS/FMS provides the initial, pilot-input flight track to        be optimized (1412)—there may be more than one flight track        option (e.g: multiple routes around, or over, terrain);    -   c. Weather information (1414) is uploaded over data link (ADS-B        in);    -   d. The aircraft data bus provides current operating or        environmental parameters (1416) including temperature, air        pressure, and if this is an in-flight update, aircraft position        and speed.        2. Data pre-processing (1420) converts the wide-area weather        information into a Weather index (1403) of interpolated weather        at the locations along the flight track (based on latitude,        longitude, and available altitudes). Similarly, sources of        caution (e.g., icing or precipitation) are pre-processed to        check for their possible effect on the intended route of flight;        data are provided in the Cautions index (1405).        3. The FPOP platform is called with the fully assembled set of        input data (step or stage 1401).        4. The Flight path generator (1404) creates a three dimensional        flight path from the provided 2D Flight track. The generated        path is defined by a set of waypoints (defined by latitude,        longitude, and altitude), that are connected by segments (climb,        cruise, descent) with speeds specified for each segment:    -   a. A library of path/performance heuristics (1407) provides        optimal climb rates, cruise altitudes, and descent rates.        Heuristics are corrected for aircraft current weight and energy        state;    -   b. The climb and descent library (1409) uses the rates (from the        heuristics) to provide climb and descent distances, which        determine intermediate waypoint locations;    -   c. Intermediate waypoints may be added to match airspace        constraints (1410), including constraints due to terrain; and    -   d. Waypoints are connected with flight segments; speeds and        range extending generator state are assigned to all segments        from the heuristics.        5. Environment evaluation (1412) examines the Flight path in        combination with the Weather and Hazards data to determine if        the path would benefit from optimization under real world        conditions:    -   a. If no additional optimization is necessary or would be        beneficial, then the path is provided to the Flight path        optimizer (1408);    -   b. If further optimization has potential benefits, then the        Alternate flight paths generator (1413) is invoked;        -   i. The Breakpoint generator (1414) may add additional            intermediate waypoints to the cruise segments based on            sources of cautions and/or winds aloft; this provides more            degrees of freedom in the optimization space;        -   ii. The altitude of each cruise segment is varied up to the            maximum (set by performance limits) and down to the minimum            (set by constraints). Speeds and energy source utilization            are again set by using the heuristics;        -   iii. The full set of possible paths is provided to the            flight path optimizer (1408).            6. Flight path optimizer (1408) varies the cruise speed and            Power ratio over the flight path to minimize an objective            function within any specified constraints. For each Flight            path, the optimizer generates an Air path, Energy plan, and            objective function. Note that a path may be discarded if no            viable Energy plan can be found.            7. All viable paths are sorted by objective function, and            the optimum path is identified and returned. Final outputs            (1430) are the Flight and Air paths, Energy plan, Required,            Reserve, and Arrival energies, and a value of the specified            objective function.            Flight Simulation Modules (Note that these Represent            Examples of a Possible Implementation)

Module Inputs Procedure Outputs ALL Aircraft weight, CG, starting,ending altitudes, atmospheric conditions (pressure, temperature), windvelocity Takeoff Flap angle, runway Calculate speeds for VCLmax, VLO,Take off speeds, distances for information (slope, V1, V2, calculateacceleration distances, ground roll, obstacle clearance, surface type)times, and balanced field requirement normal, engine out, balancedfield, per FAA regulations, terminates on initial climb rates andgradients, obstacle clearance normal, engine out, take off time, energyused, and generator run time Climb Climb type (energy/ Calculatesacceleration to climb speed, Ititial, climb rate, total time, fixed,speed) then executes a time stepping iterative energy, fuel, anddistance to climb, Speed (KIAS) calculation of either a fixed speedclimb, final altitude, final speed, generator Climb power or maximumspecific energy climb (P_(S)), run time with climb rate determined byexcess power available. Terminates at final altitude. Integrates energy,time and distance for segment totals Cruise Speed or Mach, Calculatesacceleration to cruise speed, Total time, distance, energy, fuelTermination criteria: followed by steady state cruise until burn, andgenerator run time range, or final meeting termination criteria. Singlewaypoint, or minimum DOF, iterative time stepping calculationweight/energy, of flight physics with a Shuts down the energy reserverange extending generator once required at end sufficient stored energyremains to complete flight with required reserves. Descent Descent rate(ft/sec) Calculates either a closed form solution Total time, distance,energy, fuel Final speed for a “best glide” descent (L/D max) at burn,and generator run time zero net thrust, or a time stepping, iterativedescent with fixed power, and linear deceleration from initial to finalairspeed. Terminates on final altitude Landing Flap angle, runwayCalculate landing speeds, VCLmax, Approach, round-out, flare, andinformation (slope and Vref, V_(TD). Calculate four distances; braking(ground roll) distances. surface type), approach initial descent fromobstacle clearance Time, energy, and fuel used. angle, obstacle height,to start of round-out, round-out, flare, generator run time. braking μ,residual and ground roll. Round-out uses an N_(Z) thrust value todetermine vertical, and horizontal round-out distance.

Note that the flight path optimization (such as that performed by theFPOP, and as described herein) depends on parameters which affectaircraft efficiency and cost; these vary significantly betweenconventional and hybrid platforms as shown in the table below.

Parameter Hybrid-Electric Conventional Cost of fuel Cost of fuel +battery depreciation + charging Linear function of fuel consumed energyTotal flight energy Fuel (kWh equivalent) + battery charging Fuelconsumed (kWh equivalent) energy (kWh) Propulsion energy Range extendinggenerator efficiency may Engine efficiency coupled tightly withpropulsor efficiency depend on altitude, speed, or may be efficiencyindependent of both. Combination are function of speed, altitude Storedenergy efficiency may depend on state of charge, and discharge ratePropulsor efficiency function primarily of speed Cost of engine Linearfunction of run time (constant power Varies from simple function ofoperating time maintenance output, and not equal to flight time) (sameas flight time), to comprehensive function of number of power cycles andtime weighted by hot section temperature. Optimum cruise speed Functionof two distinct operating parameters: Function of Velocity and/or Mach,and weight. for a fixed altitude Aerodynamic and propulsor efficiencyTotal energy required, P*t (where t = d/V) and total energy available(P_(gen)*t + E_(storage)) The first is a function of weight and speedand easily calculable for any given weight. The second however isspecific to the exact energy state and range requirement of the currentflight. For any given weight, and altitude, optimum For a given weight,and altitude, there is a single, speed changes with energy state andrange. minimum energy cruise speed Optimal cruise altitude Function ofrange, stored energy, flight mode, Highest altitude which can be reachedgiven the and range extending generator power with range altitude

In some embodiments, an optimization process may be conducted in orderto generate path or other heuristics for the FPOP Flight path generator,as described herein. Below is a table containing information regardingdifferences in the optimization process between that which might beperformed for the inventive hybrid-electric regional air transportationsystem and that which might be used for a conventional aircraft andtransportation system.

Optimization Process Hybrid-Electric Conventional Objective Objectivefunction may be based around the “cost Objective function is basedaround the “cost function function” C_(E)/C_(T) (cost of energy/cost oftime) function” typically C_(F)/C_(T) (cost of fuel/cost of Cost ofEnergy includes fuel burned in range time) extending generators, batterycharging energy and “Cost of Time” includes all non-fuel costs batterydepreciation. including maintenance (engine, airframe), crew, “Cost ofTime” includes all non-fuel costs including depreciation (airframe), andany other costs maintenance (engine, airframe), crew, depreciationdirectly related to flight time (e.g: insurance). (airframe), and anyother costs directly related to flight time (e.g: insurance), May alsoinclude externalities such as emissions costs Altitude Vs. Efficiencyweak function of altitude. Efficiency strong function of altitude(increases efficiency in Typical altitudes 6,000-25,000 ft withaltitude). optimization Optimizer selecting altitude for speed, notefficiency. Typical operating altitudes from 25,000 to 40,000 Climbspeeds default to higher values (shallower ft (turboprop, regional jet).climb) regardless of Flight mode (C_(F)/C_(T)) to improve Over regionalranges, optimizer is forced to trade average speed w/out efficiencypenalty; efficiency (lower fuel burn) for speed depending Optimizerbalances cost of time with efficiency of on value of C_(F)/C_(T) storedenergy utilization (which decreases at high A high C_(F)/C_(T) minimizesfuel burn, results in a discharge rates), and any sensitivity of rangesteeper climb at a slower speed to the highest extending generatorefficiency to altitude. altitude possible for the given range tominimize Maximum altitude limited either by range, range fuel burn, anda flight idle descent to maximize extending generator power available,or aircraft time spent at cruise altitude. ceiling A low value forC_(F)/C_(T) minimizes total time, Optimizing for minimum energy willresult in a flight results in a higher climb speed, lower climb angle,at speeds close to aerodynamic best Lift/Drag, with lower cruisealtitude, and earlier, powered descent minimum possible range extendinggenerator usage. to maximize average speed. Optimizing for maximum speedwill result in a low angle climb to the maximum altitude at which fullgeneration is available, with continuous range extending generator usagefrom takeoff through end of cruise. Calculation For a given altitude,weight, and range, best efficiency For a given altitude and weight, bestefficiency of best speeds results in full depletion of the stored energysources cruise speed is an easily calculated, single value by the end ofcruise. minimum between aerodynamic and engine Increasing C_(T)increases range extending generator efficiencies usage time up to thefull cruise segment (maximum Aircraft total energy is a continuousfunction of cruise speed) aircraft state (potential + kinetic) and fuelburned. For a given altitude, cruise speed is a function Thiscombination of first order, continuous aerodynamic efficiency energy andpower available, dependencies allow optimization for best cruise andobjective function. altitude with a range constraint with standard Rangeextending generator power is typically constant optimization techniques,such as energy up to a limit altitude, and then decreases; this mayminimization. Cruise altitude then determines best reduce the altitudefor maximum speed in cruise cruise speed and total energy required (fuelburn). This combination of weak altitude sensitivity to efficiency,multiple energy sources of varying properties and utilization rates, anddiscontinuous range extending generator properties with respect to timeand/or altitude results in highly coupled, discontinuous optimizationspace which is not compatible with closed form integration or linearoptimization solvers, requiring instead a nonlinear method (e.g:Neldor-Mead) coupled with flight simulation This level of optimizationwould be prohibitive as a standard flight function Instead, heuristicsare generated prior to flight, which determines an optimal path andEnergy plan starting point for no-wind operations.

FIG. 13 is a diagram illustrating an example flight path optimizationfor an aircraft that may be generated by the Flight Path OptimizationPlatform (FPOP) and used at least in part to control the operation ofthe aircraft in an embodiment of the inventive regional airtransportation system. As shown in the figure, a flight path 1300 may becomposed of one or more segments (such as those identified by “A”,“A.1”, “B”, “C”, “D”, etc. in the figure), where each segment mayrequire a specific configuration of the aircraft and control systems inorder to be properly implemented (e.g., subject to the constraintsplaced on the operation of the aircraft by travel distance, fuel(energy) level, fuel consumption, total weight, etc.). The figure showsa graphical example of the flight path optimization process in crosssection, and thus only an altitude profile as a function of distance. Inthis example, the default flight path 1300 is a single origin, singledestination path, which is broken into multiple segments by the PathGeneration module/function of the FPOP.

The initial path (represented by the dashed line) produced by the PathGeneration process of the FPOP module is based on the origin (A),destination (D), and the altitude constraint for the terrain obstacle.This default path results in an initial climb (the segment A to A*), acruise mode (the segment A* to B) at an optimal no-wind altitude, asegment at higher altitude to clear the obstacle (B to B.1), a return tooptimal cruise altitude when the obstacle constraint is removed (thesegment B.1 to C) and cruise until the top of the descent point (thesegment C to C.1), followed by the descent to landing (the segment C.1to D). The path generation process uses the climb and descent rates todetermine the intermediate points of the flight path (i.e., A.1, B.1,and C.1). Note that optimal climb and descent rates, cruise altitudesand speeds, and the generator off point (indicated by the trianglebetween points C and C.1) are determined by the Flight Mode and range.For example, a “high speed” mode over a medium range results in a bestrate climb to the maximum altitude which allows peak generation power,with range extending generators on for all cruise, whereas an economymode, over the same distance, may cruise more slowly, at a loweraltitude, and range extending generator shuts down partway throughcruise, completing the flight on stored energy alone. This path isprovided to the Energy Optimization module, and then to the PathEvaluation module of the FPOP.

Returning to the example optimization process illustrated in FIG. 13, insome embodiments (and as suggested by FIG. 14), in a typicaloptimization process, an Environment Evaluation module/function 1412checks the Weather Index 1403 and Caution Index 1405 for the potentialcruise segments and determines whether further optimization should beperformed based on the wind velocities, changes in wind direction orspeed, etc. (as indicated by the “Yes” or “No” branch of the “RefinePath?” decision step 1415 of FIG. 14):

-   -   Breakpoint Generator 1414 first determines whether the existing        cruise legs (i.e., A, B and C), need additional subdivision        based on wind gradients; in this case, the answer is no, as the        wind is consistent on each leg (as suggested by the wind speeds        W1 and W2 shown in FIG. 13);    -   Alternate flight paths generator module 1413 varies the        altitudes at A.1, B, and C, which modifies the locations of        points A.3, B.1, C and C.1 of the flight path; note that there        are a limited number of feasible variations because aircraft        regulations require cruise to occur at incremental altitudes        (e.g., every 2,000 ft in the US). The lower bound for a cruising        altitude is set by the minimum route altitude (the MEA, defined        by the terrain and airspace), while the upper bound is set by        aircraft performance capabilities. The result of this variation        process is a set of potential flight paths;    -   Each potential flight path is analyzed by the Flight Path        Optimization module 1408 by implementing a flight simulation        process to find the lowest energy usage for that path; and    -   Path Evaluation module 1402 is used to rank the paths and return        both the default path(s) and the path(s) which minimized the        objective function.

In this example (as compared to the default flight path 1300 shown inFIG. 13), Path Optimization module 1408 decreases the initial altitudeto the lower limit to avoid the head wind, moving back the location ofA.3 to ensure sufficient distance to climb to B for clearance of theterrain obstacle. The altitude at B doesn't change, but after theobstacle is cleared, a lower cruise altitude at C takes advantage of atailwind, and the top of descent point (C.1) is delayed as long aspossible to utilize the tailwind. The reduced energy usage on theinitial segment allows the generator to be shut down earlier (assuggested by the triangle nearer to point C in the figure).

The Table below shows each waypoint in the optimized path, the source ofthe intermediate waypoints, the desired altitudes and speed(s) for eachleg, and how the optimization process modified the original defaultflight path. In the table, the speed and/or altitude of the A.2, B, B.1,and C waypoints have been optimized. The table also lists how the speedsare determined for each leg; note that legs which have been optimizedfor altitude have also been optimized for speed.

ID Name Source Speed Constraint Altitude A Departure Flight Track n/aFixed Fixed point A.1 Top of Calculated Calculated by Minimum A.2initial climb rule A.2 First cruise Calculated Optimized for MinimumOptimized to lower altitude to leg Flight mode avoid the strong headwind(W1) A.3 Start of Calculated Calculated by Minimum A.2 second fromconstraint rule climb at (B) B Cruise Flight Track Optimized for MinimumConstrained by minimum altitude waypoint Flight mode required to clearterrain B.1 Cruise Flight Track (B) Minimum (B) waypoint C Start 3^(rd)Calculated Optimized for Minimum Optimized to altitude that deliverscruise leg from descent Flight mode best combination of tail wind (W2)distance and range extending generator efficiency. C.1 Start ofCalculated Calculated by Minimum (C) descent from based on rule forzero- zero net-thrust thrust descent (D) D Arrival Flight Track n/aFixed Fixed point

As noted, flight path planning for a regional hybrid-electric aircraftwith multiple power sources requires more complex trade-offs than aconventional aircraft over long ranges. For instance, optimal flightaltitude is determined by a combination of speed versus efficiencyobjective, flight distance, weather aloft, aircraft aerodynamics,available energy and relative energy storage versus range extendinggenerator or alternate power source usage. The FPOP processes enablethis optimization both pre-flight and during flight as conditionschange, to determine the optimal flight path or paths.

As described herein, in some embodiments the FPOP platform or system fora hybrid-electric aircraft may have the following characteristics and/orperform the indicated functions:

-   -   Generates one or more Flight path(s), optimized for the Flight        mode, and which meet both aircraft and environmental constraints        (e.g., final energy state, and airspace limitations). A        determined or revised Flight path may be uploaded to the FMS        (shown in FIGS. 3 and 4) to be executed by a pilot or autopilot;    -   Flight planning for a regional hybrid-electric aircraft with        multiple energy sources requires more complex trade-offs than a        conventional aircraft, and is also more critical to flight        safety due to the complexity of using multi-source energy        reserves. Aircraft performance over a mission is inherently        nonlinear and typically approached with some level of dynamic        programming (e.g. simulation), coupled with an optimization        method, for example an energy method to minimize total flight        energy. Hybrid-electric performance entails additional levels of        complexity in that energy contributions are from multiple        sources, which are physically distinct (either an energy source,        or a power source), which may not be continuous with respect to        time, or cost over the flight. This results in a complex        optimization process not addressed by conventional flight path        planning;    -   As described, the Flight Path Optimization Platform (FPOP) for        hybrid-electric powertrains typically uses a two-step        process; (1) Flight path definition to set the overall flight        profile including cruise altitudes, followed by (2) optimization        in the current operating environment.        -   Flight path definition may occur on one or two levels            depending on the environmental conditions:        -   Level 1: Initial definition of a 3D Flight path using            heuristics which provide the optimal altitudes, cruise            speeds, and Energy plan for the desired range and Flight            mode. If the flight environment is relatively simple (low            winds, no cautions or hazards), then Level 1 is typically            sufficient;        -   Level 2: Invoked to generate alternate paths when wind or            cautions adversely affect the Level 1 path. Varies the            altitude(s) of the Level 1 Flight path cruise segment(s) to            generate a set of modified paths.        -   An optimization is performed on each Flight path by            adjusting cruise speeds and the Energy plan (Power ratio) to            minimize an objective function within constraints, while            taking into account the current operating environment            (weather, and aircraft state). Results are the Air path,            Energy plan, and value of the objective function. In the            case of multiple Flight paths, the path with the minimum            objective function is returned as optimum.

Compared to conventional aircraft operating on long haul flights, theregional, hybrid-electric aircraft flight profile has many more optionsfor speeds and altitudes, and is significantly more complicated due tothe use of multiple energy sources which respond differently to altitudeand power demands, and have different costs. As part of this innovationthe inventors recognized that conventional aircraft flight planning isinadequate to provide safe, efficient flight paths for hybrid-electricaircraft, and that this capability must be provided to ensure flightsafety and reduce pilot workload. The implementation of the inventiveFPOP platform/system is based on the recognition by the inventors of thedifferences between operating and optimizing hybrid-electric powertrainsand those of conventional aircraft. These differences or distinguishingcharacteristics include:

-   -   Conventional, long haul aircraft use a limited set of prescribed        climb and descent profiles and cruise at altitudes between        31,000 and 40,000 ft. Cruise altitude is easily determined from        winds aloft and air traffic requirements, and “optimization” is        generally little more than an adjustment to speeds to adjust for        the price of fuel;        -   Regional aircraft spend a much higher fraction of the flight            path/time in climb and descent, and cruise altitudes vary            widely depending on range, weather, terrain, and air traffic            control. Even so, for conventional aircraft in regional            operations, the best cruise efficiency typically relies on            climbing to the highest altitude practical given the cruise            range;        -   Energy planning in conventional aircraft is typically the            process of ensuring that more fuel is available than is            required for the flight. Fuel burn is calculated from the            planned flight segments and the required reserves (expressed            as time, or time+diversion to alternate). Calculations are            made by the pilot or FMS using a system of table lookups            accounting for aircraft weight, cruise altitude and speed;        -   Cruise speed is chosen between a high speed cruise (maximum            power), or a long range cruise (best economy) depending on            cost of time and fuel available;        -   Conventional aircraft engines lose power with altitude, and            even a “full-power” (i.e. full throttle) flight will not            exhaust fuel reserves too quickly; and        -   Conventional flight path optimization is typically based on            a simple ratio of Fuel Cost to operating costs. For example,            some aircraft manufacturers call this the “cost index”, a            single number set by the operator, which the aircraft FMS            uses to set the climb speed, cruise speed, and top of            descent point.    -   In contrast, hybrid-electric regional aircraft are efficient        across a wide range of altitudes, have cruise speeds determined        by energy, not power available, and have a more complicated        total cost vs. energy cost:        -   Cruise altitude primarily affects speed, and power            source/range extending generator power available (which            affects range for a given speed). With much smaller changes            in efficiency; an optimizer will choose higher altitudes for            speed (minimize total cost), over energy efficiency (the            opposite of conventional flight planning)        -   Energy planning is significantly complicated by            dual/multiple energy sources with different operating            properties:            -   a. Stored energy provides a wide range of power,                independent of altitude or speed, but with relatively                limited amounts of energy. Stored energy may suffer                efficiency losses as a function of power output,                effectively reducing the amount of stored energy when                operating at high discharge rates;            -   b. Range extending generator provides constant power,                with total energy limited by fuel available. Range                extending generator power and efficiency may change with                altitude; and            -   c. Reserve energy must be specified for each source,                sufficient to ensure that safe flight can be maintained                at all times.        -   Cruise speeds range from maximum energy (total of stored            energy available for cruise+generation*time), which is a            function of range, and minimum energy; cruise speed is set            to match a target future energy state.        -   Electric propulsion does not lose power with altitude; a            pilot continuing to fly at maximum power at high altitude            will incur a much more rapid depletion of stored energy than            a conventional pilot would expect.        -   Flight path optimization trades total costs of energy and            power (stored energy costs+generation costs) against            operating costs. Differences in cost of stored vs. generated            energy extends the basic optimization to include energy            sourcing optimization (e.g., the POCS Hybrid energy planner            function).

As part of creating the inventive aircraft and regional transportationsystem, the inventors have developed a process or set of processes forthe design and optimization of forward compatible hybrid-electricaircraft. The design process includes sizing of powertrain components,propulsion integration, wing sizing, and noise reduction whichcollectively result in an aircraft with 60-80% reductions in directoperating costs, 20-30% shorter runway capabilities, and 15-25 EPNdBlower noise than conventional aircraft. Moreover, forward compatibilityensures the aircraft can accommodate future EV/Hybrid technologies viarelatively simple upgrades of specific powertrain modules. As a result,an embodiment of the inventive aircraft is expected to remaincompetitive over the target life of the airframe, offering improvedperformance and decreasing costs with module upgrades. In addition, thesame or similar process can be used to develop aircraft variants withvarying performance tailored to specific markets (via a choice ofpowertrain modules without any change to the external airframe orpropulsors). This enables the development of aircraft optimized tospecific markets with minimal engineering and re-certificationrequirements. This set of design and optimization concepts and processesfor aircraft that may be utilized as part of the inventive regional airtransport system will be described in further detail with reference toFIGS. 15 and 16. Note that conventional aircraft design processes arenot able to size the hybrid-electric powertrain components, ensure theaircraft and powertrain stays abreast of rapidly improving EV/Hybridtechnologies, or fully leverage the unique benefits of electricpropulsion, including breakthrough efficiency, short take-off andlanding capabilities and low noise operation.

FIG. 15 is a flow chart or flow diagram illustrating a hybrid-electricaircraft design process that may be used in implementing an embodimentof the inventive air transportation system. In some ways, the overallflow is similar to conventional aircraft design, but certain steps(those shown bolded) are either modified or entirely unique to thehybrid-electric design process. A table below provides a description ofeach of these changed steps, with a comparison to the conventionalprocess.

The flow chart of FIG. 15 illustrates the primary components in theinventive aircraft design cycle. Aircraft design is a highly iterativeprocess because of the interdependence of the key design parameters ofweights (payload, fuel and aircraft), propulsion power, and keystructural sizing (wing, empennage, landing gear, etc.). Note that theoperations or processes shown bolded are those significantly impacted bythe hybrid-electric powertrain and its use as part of the inventiveregional air transportation system:

1. The design process starts with top level design requirementsincluding payload, cabin size, the cruise speed and range, maximumaltitude, the takeoff and landing runway performance, and, the noise andcost requirements (step or stage 1502);2. Weight is the single most important driver in aircraft design.Maximum weight directly affects required engine power, wing size, andstructural weight, as well as cruise power (energy) required. Eachdesign cycle starts with an update to weights (step or stage 1504);3. Based on maximum weight, the aircraft wing and tail areas are sized,and a rough performance analysis is used to determine requiredpropulsion power, and energy capacity to meet range and speedrequirements. The aircraft configuration is also laid out for locationof major components, wing, tail, landing gear etc. (step or stage 1506);

-   -   a. Unique to the hybrid vehicle is powertrain component sizing,        taking into account the amount of stored energy and generation        power capacity (step or stage 1507). The 3-tier design process        described herein uses ranges and speeds, in combination with        cost, to provide the requirements and constraints needed for        this function;        4. From the sizing and configuration, weights can be built up        from a series of models and component weights (step or stage        1508). For example, wing parametric weights take into account        thickness, span, area, sweep, and taper to estimate typical        weights from the geometry, while engines and landing gear are        typically fixed, component weights provided by the supplier;        5. The sum of all aircraft weights results in the empty weight;        if empty+payload+fuel+stored energy weight exceeds the maximum        weight, then the relevant portions of the design process will be        performed again with updated weights;        6. Performance modeling (step or stage 1510) is now used to        estimate aircraft performance; this involves application of the        representative aerodynamic and propulsion models using the        weights, configuration, and powertrain information developed        from the sizing steps;        7. Note that hybrid-electric propulsion requires two independent        models; one for the propulsor, one for the powertrain (step or        stage 1511);    -   a. The propulsor model combines the motor sized in step (3),        with the aerodynamic characteristics of the propulsor (e.g, the        propeller) to calculate power required for a specified thrust        level; and    -   b. The propulsor model determines the thrust available based on        the powertrain model and includes the stored energy units and        generator. The powertrain model determines maximum power        available, and, for a given power requirement, the ratio of        storage to generation, storage discharge rate and range        extending generator fuel burn.        8. Lift and drag models are based on the geometry of the        configuration (step 3) and enable performance calculations in        various configurations, including cruise, take off, landing,        flaps up, and down, landing gear up, and down, speed brake        deployed, etc. Note that electric propulsors may be used with        regenerative braking to replace conventional spoilers;        9. Performance modeling employs physics based models which may        include numerical approximations, and time stepping methods to        calculate the time, fuel, energy, distance, and altitude change        for each step;    -   a. The performance models may be modified from conventional        versions to control and track both propulsor and powertrain        models. This includes controlling generator on/off, and tracking        fuel burn and run time, and stored energy usage; and    -   b. Costs may be calculated by applying the performance model to        a representative flight path, and applying cost values to the        integrated totals of times, fuel burn, and stored energy used.        10. Performance is now checked against design requirements;        deficiencies will require design changes, and another design        cycle (step or stage 1512).

The table below provides a description of certain of the changes to aconventional aircraft design process that were developed by theinventors for a hybrid-electric design process, along with a comparisonto the conventional process.

Area Hybrid-Electric process Conventional process Design requirementsCruise range, Define a three tiered set of ranges and speeds: Define amaximum range requirement and speed A. range and speed the aircraft canfly on stored energy to be met at long range cruise speed. alone, rangeextending generator needed only to meet Define maximum cruise speedreserve requirements. B: Optimal speed hybrid range which fully depletesstored energy in combination with range extending generators. Alsodefines minimum cruise speed when flying to the full distance. C:extended range primarily using range extending generators and flown atlower speeds Define maximum cruise speed Forward Define a set ofexpected changes in powertrain Not considered. compatibility componentsover the aircraft lifespan. Includes improvements in energy storage,power generation, and propulsion motors. Three tier range and speedrequirement re-defined at these future technology levels Net result isan “envelope” of design requirements covering current and future rangesand speeds. Cost Cost requirements specified in the 3-tier process usedCost requirements based on for speeds and ranges including forwardcompatibility, evolutionary improvement over for example: existingaircraft with small changes in A. minimum cost, up to 80% reduction overseveral areas conventional. Costs increase at shorter ranges. B: 60-70%lower DOC than conventional aircraft C: 30-60% lower DOC DOC reductionis maximized on shorter flights, the opposite of conventional Range Vs.High fixed mass for energy storage, and low fuel burn in The maximum sumof fuel weight and Payload hybrid mode results in minimal range payloadtrade; payload weight is a constant; this instead these values werealready captured: results in two cruise range Range with maximum payloadis maximum hybrid requirements: range (B) Range with maximum payloadAbsolute maximum range is the requiremen for range Absolute maximumrange as limited by (C). fuel volume Maximum Conventional propulsionlimits do not apply since motor Maximum operating altitude limited byaltitude power available is not affected by altitude. thrust lapse inconventional aircraft Other physics limits may apply; for examplevoltage engines breakdown (corona) limits maximum voltage as a functionof altitude Barring physical limit, the designer must pick a rationalceiling based on intended cruise altitudes, and level of pressurization.Runway The selection of length is same as conventional. Minimum runwaylength is selected to lengths However, motor peak power capabilitiessubstantially be the longest runway which stilll meets alter the takeoffdesign process allowing a shorter the target market requirements. runwayrequirement than an equivalent conventional aircraft without compromiseWeights Weight Same as conventional, however, for the payload fractionTop level estimation uses a Estimation to be representative, payloadweight includes all representative payload mass fraction passengers,cargo, fuel, and energy storage weight (PLF), typically between 0.55 and0.6 for regional aircraft W_total = W_Payload/(1-PLF) Payload weightincludes all passengers, cargo, and fuel Initial fuel requirements areestimated from cruise range and average fuel burn per mile.Configuration and Sizing Wing sizing, Weighted multi-point optimizationwith constraints. Wing design optimized for cruise planform Operatingpoints are: condition with constraints Hybrid cruise (multiple pointsfor full range of time Constraints: takeoff and landing variant speeds)distances (incl. balanced field C Cruise (generation only speed)requirements) Constraints are: Takeoff and landing distances (incl.balanced field requirements) Continued flight on only energy storage orrange extending generators alone. Vertical tail For a single propulsor,there is no change. For a multi-engine aircraft, vertical tail sizingFor a multiple-propulsor aircraft, vertical tail sized to sized byengine out yaw requirement. meet directional control requirements duringmaximum Yaw moment depends on moment arm motor emergency power afterpropulsor failure; this may and drag coefficient of the failed be morerigorous than a standard engine-out failure due engine in combinationwith thrust on to the very high emergency power capability. The theremaining engine(s). designer may need to trade emergency peak powerbenefits vs. vertical tail sizing. Propulsion Propulsion motors aresized independently of the Engine(s) sized by the most demanding powerpowertrain. Minimum power output determined by: of three conditions:required Take off distance with maximum (routine) peak power Take offdistance; and in case of a For a multi-engine aircraft: balanced fieldlength, with multi-engine aircraft, balanced field benefit of emergencypeak power. length. Maximum cruise speed Top of climb thrust sufficientto Minimum climb rate accelerate to cruise Power for systems isdelivered by the powertrain, and Maximum cruise speed does not affectthrust power available. The engines must be able to meet theseconditions while providing the additional power needed for aircraftsystems. Powertrain Range extending generator capacity (kW), and storedN/A; fuel volume set by range component energy capacity (kWh) are sizedas a system to meet the requirements. sizing 3-Tier range and speedrequirements including forward compatibility envelope. Performanceanalysis over standard flight profiles is needed to determine missionenergy requirements for stored and range extending generator sources.Minimum all-electric range (A) Criteria may set stored energy minimum,and must be specified in conjunction with some minimum level of kW/kgstorage density. Minimum cruise speed to full hybrid range (B) Jointlysizes range extending generator power and stored energy capacity to meetthe speed-range requirements across forward compatible envelope. Ratioof storage to generation will either be sized by constraints or costoptimization. Minimum cruise speed on range extending generators only(C) Provides a minimum sizing constraint on power generation. Anadditional safety constraint may also be applied as a requirement to beable to continue flight, including climbs, on either range extendinggenerators, or energy storage units alone in case of partial systemfailure. In all cases, the powertrain must supply not only the requiredpropulsion energy, but also the energy for all aircraft systemsincluding ECS, flight controls, landing gear, avionics, etc. PropulsionHigh power density and high efficiency over a large Maximum efficiencyrequires using the integration range of power output levels allow thedesigner to minimum number and maximum size potentially utilize numeroussmaller motors as easily as engines possible. one or two large ones. Themonolithic nature of the engines results in an aircraft design andintegration very tightly coupled to a specific engine with very fewviable engine locations on the airframe. Powertrain The hybrid electricpowertrain is distributed and Fuel system typically comprised of andenergy modular which requires sufficient space for energy multiple wingtanks, and related storage storage devices, range extending generators,fuel plumbing to interconnect and cross integration tank(s), and allrelated power electronics. feed tanks such that any engine can draw fromany fuel tank. Cooling Batteries, power electronics, motors, andgeneration all Engines and accessories are primary generate significantlevels of heat, which must be areas needing cooling, and are typicallyremoved. located in engine nacelles which have Heat generating systemsmay be embedded in the ready access to cooling flow. fuselage withoutready access to cooling flow. These heat loads vary dramatically bypower output levels from near zero to over 7% of power output. Coolingsystem should be designed to produce little or no drag across full rangeof thermal load Noise Electric motors, batteries inherently very quietNoise reduction options primarily rest reduction Range extendinggenerators integrated for noise with propulsion provider (includingreduction with compartment insulation, muffling etc. propeller ifturboprop). Electric motors ideal for integration into a ducted fanspecifically designed for low noise operation Flexibility in propulsorintegration allows more opportunities for noise reduction, by shieldingpropulsors over airframe structure, and/or keeping propulsor tip speedslow through gearing and/or motor design Performance Modeling Performancemodeling assumes that a designer experienced in the art is using one ormore performance methods to calculate aircraft performance in takeoff,climb, cruise, descent, landing, hold, etc. These methods may beempirical approximations, or may be time stepping integrations of theaircraft flight path. The following are changes required to a standardaircraft performance model to properly utilize, control, and track ahybrid-electric powertrain with electric propulsors. Propulsor Separatemodels for thrust generation and power Power and thrust generationtypically and generation unified in a single “engine model” powertrainMotor power available is only a function of electrical Engine power is afunction of altitude, models power available (I V) and is independent ofaltitude and airspeed, temperature, and usually airspeed. A simplifiedmodel may assume that the provided in large tabulated decks or motorwill put out full power when commanded, compiled subroutines regardlessof flight condition. Systems powers is pulled from the Thrust availableis calculated from the combination of engines and usually included aspart of motor power available and the aerodynamic model for the enginedeck with no additional the propulsor (e.g. propeller or ducted fan).accounting needed. This includes Range extending generator poweravailable may be overhead needed to run the engines function of altitudeand/or speed. Fuel burn is function such as fuel pumps. of rangeextending generators only. No additional losses are incurred due toStored energy discharge rate calculated from power fuel distributionrequired less generation power. Stored energy available is not afunction of altitude or speed. Stored energy model may need to addresseffect of discharge rate on energy discharge efficiency Aircraft systemspower is provided by the powertrain in addition to propulsionrequirements. Total power required is then the sum of propulsion power,systems power, and losses in transmission which are implementationspecific and may be modelled as a set of efficiencies between powersources and motors. Powertrain control includes range extendinggenerator state (on/off/ power level) either commanded or determined byrules of operation Air Brakes Regenerative braking provided bypropulsors, no Drag is produced by spoilers separate surface used, nothrust produced during (aerodynamic surface) which may be regeneration.used regardless of engine thrust. Drag is a function of regenerationpower extracted and Drag is a function of spoiler deflectionaerodynamics of the propulsor in this mode. angle and Mach number Takeoff Standard takeoff calculation is modified to include peak Forbalanced field calculations on a power (standard takeoff), and the veryrapid application multi engine aircraft there is limited or of emergencypeak power following a detected no thrust increase available onpropulsor failure. remaining engine(s) Climb Power commanded as %maximum (continuous), which Power commanded as % available doesn'tchange with altitude. Range extending (continuous), which is a functionof generators may be used for any fraction of climb from 0- speed,altitude and temperature. 100%, including shutdown of generator at aspecified energy state. Cruise Speed selected to provide desired levelof energy storage Speed selected cost and range depletion by end ofcruise. Range extending generators requirements may be used for anyfraction of climb from 0-100%, including shutdown of generator at aspecified energy state. Descent Range extending generators off,propulsion thrust (and Engines always on with minimum fuel power) may bezero, or negative providing regeneration burn and thrust, even at idlepower Flight totals In addition to standard time and distanceintegration, Track time, distance, and fuel burn hybrid-electricpropulsion system requires tracking and Engine time not usually trackedintegration of additional time and energy quantities separately-same asblock time. Energy storage units: discharge rate, total discharge, Totalenergy is the same as total fuel and remaining capacity. Also trackenergy from burn regeneration or charging from generator. Rangeextending generators: fuel burn, run time, and power generated Totalenergy consumed (including systems and propulsion) Times to trackinclude block time, flight time, range extending generator run time, andmotor peak power application times.

Note that at least the following represent changes to a conventionalaircraft design process that were developed by the inventors for ahybrid-electric design process:

-   -   Design requirements extended to enable sizing of key powertrain        components in a way that ensures compatibility with EV        technologies over the target life of the aircraft. This is        accomplished with the mentioned 3-tier set of ranges and speeds        for electric, hybrid, and extended cruise flight, specified        across a range of future EV technologies. An example of this        approach is shown in FIG. 17, with ranges and speeds for        regional operations and three levels of powertrain technology,        representing forecast performance 15-20 years into the future;    -   In contrast, conventional design requirements are typically for        maximum speed and range targets, using a specific engine which        will remain fixed for the life of the aircraft;    -   Wing design conditions and constraints extended to match the        3-tier ranges and speeds;    -   Wing design is a weighted multi-point optimization to account        for variation across the S-tier set of ranges and speeds, with        maximum cruise efficiency at the optimal hybrid speed, and very        good efficiency for climb, electric only, and extended range        cruise speeds. Conventional wing design is typically focused on        a narrowly defined long-range cruise condition;    -   Take-off performance is typically the constraint for minimum        wing size, and this is somewhat mitigated by high peak power        capacity from electric propulsion motors. Peak power may be        applied to the balanced field sizing requirement, restoring much        of the thrust lost after a propulsor failure, and dramatically        reducing the “engine out” distance to climb. This results in a        smaller, more efficient wing in cruise for a given runway        requirement, and is not available with conventional engines        which are limited to, at most, a 10% peak power increase for        emergencies;    -   An additional minimum wing size constraint unique to        hybrid-electric propulsion may be added to the design process,        which is to ensure that flight operations may be safely        continued after any one energy source failure, reducing        powertrain output capacity;    -   Propulsion system sizing includes both thrust generation        (propulsion motors) and hybrid-electric power generation (stored        energy and generation power), whereas conventional approaches        only size thrust generation;    -   Propulsion motors are typically sized by single-point        performance criteria, the common three are take-off distance,        top of climb performance, and maximum cruise speed. Electric        motors affect these sizing points;        -   Take-off power can use a peak power significantly above            maximum continuous for a limited period of time. This allows            a smaller motor to meet the same take-off requirement;        -   Motors don't lapse (lose thrust) with increasing altitude;            as a result, electric aircraft are rarely power limited at            top of climb or in cruise; and        -   This combination of features allows selection of a smaller            motor, but this may leave the aircraft with less sustained            climb rate than expected, leading to an additional sizing            point of minimum sustained rate of climb.    -   Hybrid powertrain output component sizing for stored energy and        generation power cannot be performed based on point performance        conditions. Instead, these are sized using performance modelling        over a set of mission profiles defined by the 3-tier range and        speed requirements, including future technology levels. Sizing        is determined by minimizing an objective function, within        constraints of system weight, volume, and minimum power        available from either source for safety;        -   The objective function may include one or several of the            terms below, with parameters defined by the operator:            Example Objective function=Cost of fuel+Cost of stored            energy+Cost of engine maintenance and reserves            (amortized)+Cost of battery packs (amortized)+Cost of            passenger and crew time+Cost of aircraft+Cost of emissions    -   Electric propulsion integration separates the propulsion power        available (motor) from the thrust producing propulsor (fan,        propeller). The designer sizes motor power levels with an        assumed efficiency, and then propulsors are designed to spec.        This functional separation is enabled by electric motors        operating at high efficiency regardless of size, and being        easily integrated with propellers, rotors, ducted fans etc. In        contrast, conventional propulsion engines are monolithic units        of power and thrust generation combined, and once chosen,        channel the aircraft design along the few viable paths for        integration (e.g., commercial jets always have engines under the        wings);    -   As an example, the embodiment shown in FIG. 16 features three        ducted fans for low noise and enhanced take-off performance,        with noise further reduced by shielding from fuselage and tail.        Enhanced drag reduction is accomplished through clean, laminar        wing, fuselage boundary layer ingestion, and shorter, lighter        fuselage with wake fill-in from the ducted fans;    -   Propulsion models used in performance modelling are enhanced for        the hybrid-electric design process to represent propulsion power        and thrust, power generation from multiple sources, system        efficiency losses, non-propulsive power being used, and the        ability to store energy from regenerative braking. In contrast,        conventional propulsion models are simpler, and typically        represent an engine by providing thrust and fuel burn for the        current flight condition;    -   Motor models used in the inventive system and methods provide        power consumption as a function of torque, rpm, and controller        losses. Models also represent motor capabilities for time        limited peak power outputs;    -   Power generation models used in the inventive system and methods        represent the properties of each source, and losses due to        transmission and conversion. For example:        -   Stored energy is not dependent on altitude or speed, and can            put out a wide range of power levels; however, high            discharge rates are inefficient, reducing the total energy            available, and peak power output decreases as the stored            energy level drops;        -   Generated energy consumes fuel to provide power at a fixed            level; in contrast, power and fuel efficiency are typically            altitude dependent in conventional models; and        -   Efficiency factors are specified for losses in power            electronics and wiring;    -   A propulsion model may include the availability of regenerative        braking, using the propulsors to recharge stored energy on        descent, including the losses from motor and controller        efficiency, power transmission and conversion, and stored energy        charging efficiency;    -   Performance modelling methods are enhanced to separately control        and track power output (and power generation). Conventional        performance methods control engine power, and track fuel burn.        With the hybrid-electric powertrain, the model controls motor        power, range extending generator state (on/off/power output),        stored energy power (charge or discharge), and tracks stored        energy used, fuel burn, and range extending generator run time        (which is different from flight time). These changes to the        methods are needed to analyze hybrid-electric aircraft        performance, and to use performance modelling for powertrain        component sizing and optimization; and    -   Performance modelling methods may be further enhanced to        incorporate rules of powertrain operation such as “stored energy        first”, and “generation-off during descents”.

The inventive range-optimized hybrid-electric aircraft which is designedfor maximum efficiency in regional operation may incorporate one or moreof the following features, techniques, aspects, or elements, whichcollectively enable a 60-80% lower DOC than conventional aircraft:

-   -   Capacity of the energy storage units and the output of the        range-extending generator are optimized for maximum efficiency        over regional ranges. This results in 60-80% lower DOC than        conventional aircraft, via stored energy units at 12-20% of        maximum weight of the aircraft, and range-extending generators        operating at less than 70% of maximum continuous output of the        powertrain. This is in contrast to less efficient or practical        designs for hybrid aircraft that are focused on longer ranges,        and yield <30% reductions in DOC over conventional, based on        lower stored energy capacities, and higher generator outputs;    -   Aircraft designed to minimize an objective function across the        3-tier requirements, primarily weighted for hybrid cruise        requirements (B);        -   the objective function may include one or several of the            following terms, with parameters defined by the operator:            Objective function=Cost of fuel+Cost of stored energy+Cost            of engine maintenance and reserves (amortized)+Cost of            battery packs (amortized)+Cost of passenger and crew            time+Cost of aircraft+Cost of emissions;    -   The previously mentioned 3-tier set of speed and range design        requirements is used for powertrain and aircraft design, an        example of which is shown in FIG. 17. In one embodiment, these        tiers are defined by:        -   Range A: Highest efficiency (80+% lower DOC than            conventional aircraft) and optimal speed over electric-only            range.        -   Range B: Intermediate efficiency (60-70% lower DOC than            conventional aircraft) and optimal speed over larger hybrid            range.        -   Range C: Good efficiency (30-60% lower DOC than conventional            aircraft) and lower speeds beyond to maximum range            determined by onboard stored energy and fuel less safety            reserves.    -   As an example of the inventive design process, the table below        compares fuel burn between a conventional turboprop and a range        optimized hybrid-electric for each phase of a regional flight.        Note that the hybrid fuel burn is 72% lower than the turboprop        for the full flight, with reductions of nearly 90% in take-off        and climb, 67% in cruise, and 88% in descent and landing;    -   The inventive aircraft is designed for efficient operation at        lower altitudes, with a target of a 50-90% lower fuel burn than        conventional aircraft. As noted, regional operations typically        involve a higher fraction of the flight time in climb or descent        and low altitude cruise compared to conventional long range        aircraft. This imposes a much greater emphasis on operational        efficiency during these phases. Accordingly, the inventive        hybrid-electric aircraft are designed for a 70-90% lower fuel        burn in climbs and descents than conventional aircraft, and a        50-80% lower fuel burn in cruise at altitudes of 4,000 to 30,000        ft. and speeds of 150 to 400 mph, than conventional aircraft. In        some embodiments, this is accomplished by one or more of the        following:    -   Propulsion by electric motors which deliver high efficiency        independent of altitude or speed, and do not consume energy when        not under load. In contrast, aircraft gas turbines suffer from        30-50% lower efficiency at lower altitudes and speeds, and        require a minimal fuel burn even at flight idle;    -   The aircraft is designed to maximize flight on stored energy        units to extent possible, given the lower total cost relative to        the range-extending generators. This translates into outstanding        low altitude, low speed performance given stored energy units,        e.g., battery packs, which offer very high conversion        efficiencies that are independent of altitude or speed. This is        in contrast to aircraft engines wherein fuel efficiency is        highly altitude and speed dependent;    -   The pairing of the propulsion motors with low pressure        variable-pitch propellers or ducted fans that are designed for        high efficiency across a range of low and intermediate speeds        (e.g., 150-300 mph) typical of regional operations. In        particular, these provide far greater efficiency in climb, or        low altitude cruise than a conventional turbofan;    -   The aircraft is designed for very high efficiency during near        airport operations, e.g., taxi, takeoff, approach, landing, with        a target of a >90% reduction in fuel burn compared to        conventional aircraft operating in these modes;    -   Taxi, approach and landing are designed to be electric-only,        utilizing the highly efficient stored energy units. Unlike the        necessary minimum fuel burn of aircraft gas turbines,        hybrid-electric aircraft consume no fuel in these phases given        that the generator is switched off;    -   Descents designed to be flown at zero energy, with generators        turned off, unlike conventional aircraft engines which require        sustaining fuel burn at idle;    -   Steeper descents are enabled by regenerative braking of the        electric propulsors, enabling energy recovery, unlike the use of        drag producing devices such as spoilers in conventional        aircraft; and    -   Take-off uses a combination of stored energy units and        generators, translating to much lower fuel burn than        conventional aircraft;    -   The aircraft is designed for quiet, short take-off and landing        (STOL) operations with 15-25 EPNdB lower noise of operation, and        requiring runways 20-30% shorter than conventional aircraft,        both with minimal impact on cruise efficiency;    -   The aircraft is designed for 15-25 EPNdB lower noise as measured        by standard CFR 14 part 36 criteria. This is accomplished by        design to limit and suppress noise generation across the three        primary sources of aircraft noise; power generation, thrust        generation, and airframe:        -   Power generation noise is reduced significantly given the            use of electric propulsion motors, and energy storage units            which produce no significant noise. Meanwhile, the            range-extending generator is downsized to <70% of maximum            continuous power and integrated in a noise insulated chamber            within the airframe, e.g., embedded in the rear fuselage;        -   Thrust generation noise is reduced significantly by the use            of low-noise variable-pitch propulsors, such as low RPM,            quiet propellers, or variable-pitch ducted fans. In            addition, propulsors may be integrated in the airframe in            ways that shield noise from propagating to the ground, e.g.,            using aircraft wings, fuselage, or empennage flight            surfaces; and        -   Airframe noise is reduced significantly via regenerative            braking with the low-noise propulsors instead of            conventional spoilers;    -   Aircraft operations may be optimized for further noise reduction        by leveraging unique features of the hybrid-electric powertrain:        -   Quiet taxi, descent and landing on energy storage units,            with generator switched off;        -   Take-off noise reduced with a shorter ground roll and steep            angle climb-out over noise sensitive areas. This is enabled            by the high peak power capability of the electric propulsion            motors, and by use of a low-noise ducted fan for high static            thrust; and        -   Approach and landing noise are reduced by steep, controlled            descents with regenerative braking, using the variable pitch            electric propulsors;    -   The aircraft and associated flight operations are designed for        use with 20-30% shorter runways than conventional aircraft by        leveraging features of the hybrid-electric powertrain to        accomplish this without the typical performance penalties.        Similar STOL performance in conventional aircraft would require        larger wings and engines, resulting in reduced efficiency and        payload;    -   The design achieves a thrust boost during take-off by leveraging        peak output capability of the electric propulsion motors,        thereby enabling STOL operations without a need to upsize motors        (e.g., a 20% boost over continuous output for 2-4 minutes during        takeoff and initial climb);    -   The design achieves a shorter balanced field without larger        wings or engines. “Balanced field” calculates maximum runway        required following an engine failure during takeoff, and        balances the distance required to either stop on the runway, or        continue the takeoff on the remaining engines up to an obstacle        clearance height (FAA standards are 35 or 50 ft). Balanced field        (and hence required runway) is dominated by rate of climb on the        remaining engine(s); as part of the innovative system, climb        distance following a failure is dramatically reduced by boosting        surviving propulsors up to 200% in the event of a partial or        complete failure, and stopping distance is reduced by rapidly        dropping thrust to zero or negative (thrust reverse). Detection        of failures and the boosting of thrust to compensate are managed        automatically by the inventive powertrain optimization and        control system (POCS). Similar thrust over-boost systems in        conventional aircraft are limited to <10% boost, while stopping        distances are hindered by spool-down time and thrust residuals        on surviving engines;    -   In the event of a partial or complete failure of a propulsor,        e.g., due to a bird strike, or loss of one or more propulsor        motors in flight, the POCS boosts power to the surviving        propulsors to compensate for a limited period, thereby enabling        an extended reaction time window for the pilot to take        corrective action, and providing safe descent to a nearby        airport or landing area;    -   Unlike the limited boost capabilities of conventional aircraft        engines, electric propulsion motors can boost up to 200% of        continuous power for limited time periods, typically determined        by the system's thermal limits; and    -   Variable-pitch propulsors coupled with electric motors enable        very quick reduction of thrust to zero, translating to shorter        stopping distances than aircraft gas turbines given spool-down        time and thrust residual effects.

As mentioned herein, the inventive aircraft and design process areintended to provide forward compatibility across the airframe,powertrain and propulsion system(s). This is accomplished byincorporation of several underlying principles or design guidelines:

-   -   The aircraft is designed to accommodate upgrades to future EV        technologies over the life of the airframe, including improved        flight performance enabled by the upgrades. Given the rapid        evolution of EV technologies, this feature ensures the aircraft        remains competitive over time as technologies improve (e.g.,        batteries, supercapacitors, electric motors, internal combustion        engines, fuel cells, etc.). In addition, this feature enables        the aircraft to transition smoothly from hybrid-electric to        all-electric once energy storage technologies improve to the        point where range-extending generators are no longer required.        The ability to upgrade components of a hybrid-electric        powertrain for step-change performance improvement is unique to        the inventive hybrid-electric aircraft, and a contrast to        conventional aircraft which have largely monolithic engines;    -   To ensure forward compatibility, the inventive hybrid-electric        aircraft are designed at multiple points, with a powertrain        sized for speed and the 3-tier range requirements (A), (B)        and (C) noted, but are based on technologies available at        aircraft launch and forecast to be available over its target        life (including a potential transition from hybrid-electric to        all-electric for some designs). This leads to a forecast for the        onboard powertrain, and in turn, determines performance        characteristics over time, such as speeds, electric and        hybrid-ranges and operating costs (with the expectation of        electric-ranges increasing and operating costs decreasing as        technologies improve);    -   Aircraft are designed for multiple discrete powertrains,        reflecting forecast upgrades to improved EV technologies over        the target design. For instance, these could include energy        storage densities changing from 300 to 1,200 Wh/kg, motor power        densities from 4.5 to 10 kW/kg, and internal combustion engine        power densities from 1 to 5 kW/kg. The aircraft design cycle is        repeated for each of the discrete powertrains, by adjusting the        3-tier range and speed requirements for the progressively        improving EV technologies;    -   In the example shown in the table below, each row represents a        discrete powertrain based on EV technologies available at a        point in the future. For each discrete powertrain, the speed and        range design requirements (A), (B) and (C) may be determined by        minimizing an objective function, for example (DOC+I+COT). These        individual requirements define a lifetime envelope of design        points including speeds, ranges, altitudes, that the aircraft        must be designed for over its target lifetime;

Range: B C Storage Motor ICE ICE A B min C min Density Density Densityefficiency electric Hybrid speed Range speed (Wh/kg) (kW/kg) (kW/kg)(BSFC) (miles) (miles) (mph) (miles) (mph) 350 5 1.1 0.35 80 400 220 700205 600 7 1.4 0.33 140 500 250 750 220 1000 8 1.4 0.33 235 550 270 850225

-   -   The airframe and propulsor are designed to operate efficiently        across this lifetime flight envelope, typically translating to        faster and higher flight over time (as shown in FIG. 17), as        energy storage technologies improve; and    -   One outcome of the design process described herein is the        recognition that forward compatibility typically limits the        weight of the rechargeable energy storage units to 12-20% of the        aircraft weight, so that payload capacity is roughly uniform as        EV technologies improve. Higher weight fractions would lead to        aircraft that are larger and heavier than aircraft of similar        payload in the initial years, with payload increasing over time,        while lower fractions lead to suboptimal efficiencies given much        higher use of range-extending generators.

As described, in some embodiments, the inventive hybrid-electricaircraft are designed to integrate with a modular hybrid-electricpowertrain, including features to ensure the powertrain can accommodatea range of EV technologies by relatively simple replacement ofcompatible modules (such as rechargeable storage units, range-extendinggenerators and electric motors). This may be accomplished by designingthe airframe with bays that accommodate a range of current and forecastmodules, along with access for module replacement. Compatible modulesare those that are designed for operation with the powertrain platform,and that are supported by the design of the aircraft. These may includestandard and extended energy storage units, high and low power rangeextending generators, and alternative energy storage technologies. Suchfeatures may include:

-   -   Multiple bays designed to accommodate rechargeable energy        storage units, standard or extended, not all of which may be        utilized on any particular flight, and some of which may be        multi-use space (e.g., generator, storage unit, fuel tank, or        cargo). Each bay provides structure, wiring, and access to        enable quick install or removal of the storage units. These        could include combinations of the following (some of which are        shown in FIG. 5):        -   Internal to the wing; standard and extended;        -   External to the wing in aerodynamic pods;        -   In mid fuselage, positioned under main cabin; and        -   In the rear fuselage, in addition to, or replacing            generators or cargo;    -   The modular energy storage bays may be integrated directly into        the primary aircraft structure, for example the wing spar box,        such that the modules serve a dual purpose of energy storage        containment and primary load path. Presence of energy storage        units within the modules may further enhance the strength of the        primary structure for increased structural efficiency and        reduced weight;    -   Energy storage units or other systems which require cooling may        utilize the aircraft skin for heat rejection. This cooling may        occur through passive contact, or may be enhanced through        circulation of coolant between heat sources and heat rejection        coils in contact with the skin;    -   The range extending generators may be integrated in modular bays        designed to accommodate generator alternatives, upgrade and        removal of the generators, and use of the bay to house energy        storage units instead or in addition to the generators. This may        be accomplished by sizing the bay, providing access, structural        support, and supporting infrastructure (e.g., fuel lines,        cooling, wiring, etc.). Generators bays may be positioned in one        or more of several locations:        -   Fuselage bay aft of the main cabin;        -   Wing mounted nacelles; or        -   Non-structural fairings; and    -   Propulsors are designed for upgrades to higher efficiency, or        higher power motors, which may include a new fan. Unlike        conventional engines, this is accomplished with minimal        (re)engineering.

Note that aircraft variants with performance tailored to differentmarkets are readily enabled by the modularity of the hybrid-electricpowertrain. The separation of thrust generation (by the electricpropulsors) and power generation (by the hybrid-electric powertrain)enables development of aircraft variants with widely varying performancevia tailoring of powertrain modules to the application, coupled in somecases with a change in the propulsors. This enables development ofaircraft with widely varying performance, speeds, ranges and operatingcosts, based on the choice of powertrain modules and propulsors. Giventhe resulting limited impact on aircraft handling and maximum weights,the (re)engineering and certification required is modest. This is incontrast to conventional aircraft where variants require significantengineering and certification re-work. In some embodiments, thedevelopment of aircraft variants may occur by the following process:

-   -   Hybrid-electric aircraft variants may be developed by modifying        the baseline aircraft via a compressed aircraft design process,        focused on access, interior layout, pressurization, cockpit, and        performance. In such a case, the following steps/stages may be        used to design a variant:        -   Define interior configuration and payload requirements;        -   Define the cockpit configuration, for example, a manned            system with provisions for unmanned operation in the future.            The following types of aircraft control may be supported:            -   Fully piloted;            -   Piloted with remote backup—primary control by one or                more pilots onboard the aircraft, and equipped for                secondary control by a remote pilot;            -   Remotely piloted—equipped for primary control by a                remote pilot, with or without assistance onboard; or            -   Fully autonomous—equipped for primary flight without                human control, and may be equipped for secondary control                by a remote or onboard pilot; and    -   Specify the performance requirements for the target market        ranges and operating conditions (such as the 3-tier (A), (B)        and (C) ranges/design requirements described herein), including        variance with technology level, and optimize the powertrain to        meet these requirements using mission analysis with the        aerodynamics and propulsion of the baseline aircraft.

The following represent examples of aircraft variants that may bedesigned and implemented using the described methodology:

Example 1 Commercial Variant

-   -   Cabin configured for economy seating, passenger baggage        allocation in line with standard for commercial carriers.        Baggage space in interior of cabin and in hold;    -   Control system configured for minimum of single pilot with        remote pilot as backup, with option for second pilot, if        required or trainee;    -   Upper range limit is point where passenger would switch to        commercial jet travel as more time and cost efficient.        Infrequent extended range operations;    -   Market segment highly sensitive to (DOC+I), less sensitive to        COT; therefore matched with lower cost range-extending generator        (e.g., TDI) aligned with slower design speeds. Pressurization to        lower altitudes, except on variants for use on very short legs        (<200 miles); and    -   The sample speeds, ranges, and resulting powertrain        configuration shown in FIG. 17 are representative of this class        of aircraft.

Example 2 Business Variant

-   -   Cabin configured for business seating, baggage allocation above        standard for commercial carriers. Baggage space in interior of        cabin and in hold;    -   Control system configured for minimum of single pilot with        remote pilot as backup, with option for second pilot, if        required or trainee;    -   Less predictable routes, more frequent use of extended range;    -   Highly sensitive to COT, less sensitive to (DOC+I); variant may        be matched with a higher power range-extending generator (e.g.,        aircraft gas turbine) aligned with higher design speeds and        altitudes for extended range cruise; pressurization to        intermediate altitudes; and

Example 3 Cargo Variant

-   -   No pressurization, or cabin furnishings;    -   Control system configured for pilot optional flight, with        control by remote pilot on unmanned legs;    -   Speeds and ranges specified to target niche between ground        transport and commercial aircraft, typically 200-700 miles,        intermediate speeds;    -   Market segment highly sensitive to (DOC+I), least sensitive to        COT; therefore matched with lower cost range-extending generator        (e.g., TDI) aligned with slower design speeds unless required by        longer range requirements; and

As described herein, the inventive aircraft are designed for safety andfault tolerance exceeding stringent aviation requirements (FAA and EASA)via a powertrain architected for graceful degradation. This includes theability to tolerate failures in power sources (energy storage units,generators), motors (propulsion, generator), convertors (inverters,rectifiers, DC-DC convertors), distribution (buses, wiring), controls(sensors, communication), as well as safety in the event of moderate orsevere impact on the system.

The inventive aircraft and powertrain operation are designed for optimalefficiency over regional ranges; this is due in part to the flight pathoptimization process implemented by the FPOP and the operation of thepowertrain for optimal efficiency, and may further include energyrecovery through regenerative braking, and center of gravity adjustmentthrough stored energy positioning for drag reduction. These aspects aredescribed further in the following:

-   -   Flight efficiency is improved by flight path optimization        capabilities unique to the hybrid-electric aircraft, including        efficient flight at low altitudes, and stored-energy first        utilization. Optimization is accomplished through the Flight        Path Optimization Platform (FPOP), described herein. This        contrasts with conventional flight path optimization in which        efficiency is strongly dependent on altitude and there is little        opportunity for flight path modifications other than to fly as        high as possible;    -   Within the optimized flight path, powertrain is operated for        optimal efficiency as described herein;    -   The powertrain is designed for energy recovery via regenerative        braking of the propulsors, as described herein. Conventional        aircraft have no way to recover energy from drag producing        devices such as spoilers; and    -   The stored energy units in the fuselage may be used to adjust        the aircraft center of gravity (CG) to simplify loading, and to        reduce drag in cruise mode. The aircraft payload weight should        be distributed such that the CG is within an established        envelope close to the center of lift, and within the envelope,        aircraft drag is reduced by moving the CG aft. Being able to        relatively quickly adjust CG location allows the operator        efficiency gains by speeding the loading process, and reducing        drag;        -   CG movement with stored energy units may be accomplished by            providing a series of bays along the fuselage, and            selectively utilizing only a fore or aft location. Another            implementation has energy storage units mounted on tracks            allowing fore and aft translation as commanded by the pilot            or flight control system;        -   Conventional aircraft may have some capability to move CG            with selective utilization of different tanks in the fuel            system, but once the fuel is burned off in flight, the            benefit is reduced and typically lost.

The Table below contains certain parameters for an example of ahybrid-electric aircraft designed in accordance with the principles andprocesses described herein. The 4-view of FIG. 16 shows a concept 40person/seat regional hybrid-electric aircraft designed using theinventive HEV aircraft design process. Overall size and weight aresimilar to the conventional ATR-42-500 (48 seats, twin engineturboprop). Given energy requirements, design of the aircraft is basedon battery energy densities ranging from 600 Wh/kg to 900 Wh/kg. Theseenables an electric range of 170-280 nm, hybrid of 425-500+ nm, atminimum cruise speed of 380 KTAS, and cruise altitudes between 18,000and 25,000 ft.

Note that the aircraft illustrated in FIG. 16 is pictured in onepossible configuration for an aircraft meeting the general requirementsstated. In this example, three integrated electric ducted fan propulsorsare used to provide thrust, and the position over the aft fuselagereduces drag through boundary layer ingestion and wake momentum deficitrestoration. Pods at the base of the vertical tails house the gasturbine generators; the inlet and exhaust are faired over when thegenerators are not running to reduce drag. The subcritical cruise Machvalue allows use of a light weight, straight wing, and the propulsorlocation on the tail allows short, lighter weight landing gear. Noisereduction may be achieved through quiet ducted fans with additionalreductions due to mounting above the fuselage and between the tails,blocking much of the fan tonal noise. The weights, sizes and performanceof the aircraft designed are below, including improvements enabled byfuture higher energy-density batteries.

Size Propulsion and powertrain Wing span 75.15 ft Powertrain typehybrid-electric Wing area 520 ft{circumflex over ( )}2 Propulsion motor3 × 1600 SHP Overall length 62 ft Power loading 7.92 lbs/hp Overallheight 20 ft Ducted fan Variable-pitch fan Cabin length 34.8 Ft Fanblades 16 Cabin height 74 In Range extending generators 2400 SHP Cabinwidth 98 In Generator 1800 kW Number of passenger 40 cont seats Maximumcruise fuel burn 1080 pph Pilots 2 Weights Stored energy Maximumtake-off weight 38000 lbs Battery mass, Cell weight 2500 Kg Maximumuseful load 500 lbs Battery mass, Pack weight 3000 Kg Maximum fuelcapacity 2500 lbs Total stored energy, new 2250 kWh Wing loading 73 PSFTotal stored energy, 1000 cycles 1912.5 kWh Take-off and Landing Cruiseperformance Take off ground roll 1100 ft Stored energy density 600 900Wh/kg Clear 50′ lobstacle 1500 ft Energy Capacity 1500 2250  kWh Maxrate of climb, SL 2400 fpm Standard cruise 335 355 KTAS Stall speed,Clean 120 KIAS maximum cruise 380 380 KTAS Stall speed, Full flaps 65KIAS Long range cruise 320 340 KTAS Landing distance over 1300 ft Hybridrange 425   500+ Nm 50 ft Electric range 170 280 Nm Flap system Activehigh liftThe table indicates several of the unique aspects of the hybrid-electricdesign. Fuel burn and fuel capacity are less than half of theconventional equivalent. Cruise performance is given for two levels ofstored energy, 600 and 900 Wh/kg; this level of improvement would beexpected over 4-8 years of aircraft operating life depending on advancesin energy storage technology. Lastly, the maximum cruise speed is muchhigher than might be expected, with propulsion motors retaining fullpower at altitude.

As mentioned, FIG. 17 is a diagram illustrating the efficiency of acertain aircraft and propulsor configuration as a function of flightaltitude and required power. The curves illustrate how an aircraft whichis energy (not power) limited will be able to cruise at successivelyhigher speeds and altitudes as the energy limits are increased. Theenvelope extends from an initial cruise speed on the order of 200 KTASwith initial energy storage density on the order of 350 Wh/kg,increasing to over 260 KTAS as storage density improves to 900 Wh/kg, a2.6× change which is expected to occur over about 10 years given currentrates of energy storage technology improvement. As part of thisinnovation, it is recognized that this performance improvement will onlybe available to the operator if the higher speeds and altitudes areincluded as design points from the beginning of the design process(rather than limit to initial performance, as would be done withconventional propulsion).

FIG. 18 is a diagram illustrating several regional zones and theassociated airports or landing areas that may be used as part ofimplementing an embodiment of the inventive regional air transportationsystem. As shown in the figure, each regional zone (e.g., “PacificNorthwest”, “Pacific Southwest”, etc.) may contain multiple landingstrips and/or formalized airports (as indicated by the dots within theregions). Note that each regional zone may contain tens to hundreds ofpotential airports or take-off/landing sites for the inventive aircraft,and may contain a regional hub or other form of centralized location.Aspects of the control of the regional air transportation system may belocated at one of several data centers or scheduling/flight monitoringfacilities. Such facilities may operate to individually and/or inaggregate to schedule flights at multiple airports, generate flightplans/paths and the corresponding instructions for one or more aircraft,communicate such instructions to one or more aircraft, and monitor theflight and its flight data for one or more aircraft.

The inventive hybrid-electric air transportation system offerssignificantly lower door-to-door travel times and lower total costs permile than alternate regional travel modes such as highways, rail orhigh-speed rail, or conventional air. This is achieved via convenienthigh-frequency “close-in” flights to a large number of regional airportsnear communities and population centers, using quiet range-optimizedhybrid-electric aircraft. Additional beneficial features of the systeminclude:

-   -   The availability of airport onsite electric energy generation        and storage. Many of the airports may be equipped with onsite        electricity generation and storage facilities to minimize        electricity costs. Onsite generation, e.g., solar, wind, etc.        may be used to recharge aircraft batteries and power the        airport, delivering excess to onsite storage or to the        electrical grid. Onsite electric storage will enable optimal        purchases of electricity from the grid (e.g., at off-peak rates)        and storage of electricity generated onsite for later use.        Retired aircraft batteries could be used in onsite storage        through late-life prior to disposal; and    -   A variety of cost-effective last-mile ground travel options at        the airports, from origin and to destination. The regional        airports may offer passengers a greater variety of ground        travels options than are offered at non-hub airports today.        Several powerful trends playing out currently will encourage        this: electric and autonomous vehicles (e.g., Tesla, Google,        Uber, Apple), ride sharing (e.g., Lyft, Uber, Sidecar,        RelayRides), fractional car rentals (ZipCar, Hertz-on-demand).        Some regional airports today are already connected to local mass        transit; over the next 5-10 years, electric and autonomous        shuttles will enable a larger fraction of airports to offer        inexpensive connectivity to mass transit. This will be        supplemented by multiple personal auto and taxi alternatives        enabled by the trends above, for example, pick-up by autonomous        cars, fractional rentals, and various forms of ride sharing.

In accordance with one embodiment of the invention, the system,apparatus, methods, elements, processes, functions, and/or operationsfor enabling the inventive aircraft, transportation system, and aircraftcontrol system or transportation system control system may be wholly orpartially implemented in the form of a set of instructions executed byone or more programmed computer processors such as a central processingunit (CPU) or microprocessor. Such processors may be incorporated in anapparatus, server, client or other computing or data processing deviceoperated by, or in communication with, other components of the system.As an example, FIG. 19 is a diagram illustrating elements or componentsthat may be present in a computer device or system 1900 configured toimplement a method, process, function, or operation in accordance withan embodiment of the invention. The subsystems shown in FIG. 19 areinterconnected via a system bus 1902 (as may also be one or more of thesubsystems illustrated in FIGS. 4 and 5). Additional subsystems includea printer 1904, a keyboard 1906, a fixed disk 1908, and a monitor 1910,which is coupled to a display adapter 1912. Peripherals and input/output(I/O) devices, which couple to an I/O controller 1914, can be connectedto the computer system by any number of means known in the art, such asa serial port 1916. For example, the serial port 1916 or an externalinterface 1918 can be utilized to connect the computer device 1900 tofurther devices and/or systems including a wide area network such as theInternet, a mouse input device, and/or a scanner. The interconnectionvia the system bus 1902 allows one or more processors 1920 tocommunicate with each subsystem and to control the execution ofinstructions that may be stored in a system memory 1922 and/or the fixeddisk 1908, as well as the exchange of information between subsystems.The system memory 1922 and/or the fixed disk 1908 may embody a tangiblecomputer-readable medium.

Note the following variables, parameters, and units are understood asbeing used in the description of embodiments of the inventive regionalair transportation system.

Variable Units Definition Stored Fuel Usable energy kWh kg Usable storedelectrical energy and fuel onboard the aircraft Available energy kWh kgUsable energy less Reserve energy Required energy kWh kg Energy neededto fly a defined Flight 

Arrival energy kWh kg Predicted Available energy after landing at thedestinal Safety reserve kWh kg Energy which should remain at arrival toprovide safe and legal reserves Contingency reserve kWh kg Additionalreserve to account for flight uncertainty Reserve energy kWh kg Sum ofSafety reserve and Contingency reserve Airspeed m/s Indicated airspeedAircraft CG m Location of the longitudinal center of gravity fromreference datum Aircraft speed m/s Inertial speed Aircraft weight kgTotal weight of the aircraft Ambient pressure Pascals Atmospheric airpressure Ambient temperature Degrees Celsius Atmospheric air temperatureAPU Generator power kW Instantaneous power output from all generationsources Battery power kW Instantaneous power output from all batterysources Caution index integer Index to table look up of potential flighthazards (eg: turbulence) Constraint type integer Altitude constraint,options are: fixed, min, max Display mode Calibration, Flight prep,Inflight control, Diagnostics Duct exit area % Percent adjustable ductexit area reduction: 100% min, 0% max Flight duration s Time from startof take-off roll to end of landing roll Flight mode Optimal, High speed,Economy,. Fuel flow rate liters/s Rate of fuel consumption by thegenerators(s) Hazard Potential en route flight hazards, e.g., icing,turbulence, precipitation KCAS nm/hour Knots Calibrated Airspeed: thecorrected airspeed read out to the pilot KTAS nm/hour Knots TrueAirspeed: inertial speed, equals ground speed in no wind Motor power kWPower delivered to the propulsor at the shaft of the electric drivemotor(s) Motor regen RPM RPM Rotational speed of the motor(s) when inregeneration mode Motor regen torque Nm Torque delivered by thepropulsor to shaft of the electric drive motor(s) Motor RPM RPM Motorrotational speed Motor torque Nm Torque delivered to the propulsor atshaft of the electric drive motor(s) Nautical mile or Nm 1,852 metersPilot generator on-off integer Generator state request from direct pilotcontrol: On or Off Pilot generator power kW Generator power delivery, asrequested by pilot control Pilot power % Propulsor power output viapilot movement of the Power lever Pilot regen braking % Pilot commandedregen braking, with brake pedals (ground operation) Pilot reverse power% Pilot commanded reverse thrust (ground operation) Propeller bladepitch angl degrees Propeller blade angle, automatically adjusted Segmenttype integer Flight segment type: take off, climb, cruise etc.Uncertainty factor % Pilot confidence in flight plan and conditions (eg.weather forecast) Weather index integer Index to table look up ofweather conditions Flight track Latitude Longitude Altitude Alt min Altmax Constraint type Waypoint 1-N degrees degrees m m m Integer FlightPath Latitude Longitude Altitude Speed Segment type Waypoint 1-N degreesdegrees m m/s integer Air path Segment Distanse Altitude Speed typeWaypoint 1-N m m m/s Integer Energy Stored plan Energy Fuel Power ratioGenerator available available (Storage/ power generation) Waypoint 1-N %full kW % full kW % kW Weather index Latitude Longitude AltitudeDirection Speed Temperature Waypoint 1-N degrees degrees m degrees m/sCelsius Cautions index Latitude Longitude Alt min Alt max HazardWaypoint 1-N degrees degrees m m integer Aircraft Available SafetyContingency Flight uncertainty state energy reserve reserve WeightAircraft CG mode factor Current kW, kg kW, kg kW, kg kg Aircraft CGInteger %

indicates data missing or illegible when filed

It should be understood that the present invention as described abovecan be implemented in the form of control logic using computer softwarein a modular or integrated manner. Based on the disclosure and teachingsprovided herein, a person of ordinary skill in the art will know andappreciate other ways and/or methods to implement the present inventionusing hardware and a combination of hardware and software.

Any of the software components, processes or functions described in thisapplication may be implemented as software code to be executed by aprocessor using any suitable computer language such as, for example,Java, JavaScript, C++ or Perl using, for example, conventional orobject-oriented techniques. The software code may be stored as a seriesof instructions, or commands on a computer readable medium, such as arandom access memory (RAM), a read only memory (ROM), a magnetic mediumsuch as a hard-drive or a floppy disk, or an optical medium such as aCD-ROM. Any such computer readable medium may reside on or within asingle computational apparatus, and may be present on or withindifferent computational apparatuses within a system or network.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and/or were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thespecification and in the following claims are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The terms “having,” “including,”“containing” and similar referents in the specification and in thefollowing claims are to be construed as open-ended terms (e.g., meaning“including, but not limited to,”) unless otherwise noted. Recitation ofranges of values herein are merely indented to serve as a shorthandmethod of referring individually to each separate value inclusivelyfalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orclearly contradicted by context. The use of any and all examples, orexemplary language (e.g., “such as”) provided herein, is intended merelyto better illuminate embodiments of the invention and does not pose alimitation to the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to each embodiment of the presentinvention.

Different arrangements of the components depicted in the drawings ordescribed above, as well as components and steps not shown or describedare possible. Similarly, some features and sub-combinations are usefuland may be employed without reference to other features andsub-combinations. Embodiments of the invention have been described forillustrative and not restrictive purposes, and alternative embodimentswill become apparent to readers of this patent. Accordingly, the presentinvention is not limited to the embodiments described above or depictedin the drawings, and various embodiments and modifications can be madewithout departing from the scope of the claims below.

That which is claimed is:
 1. A hybrid-electric power source aircraft,comprising a source of energy, the source of energy including a sourceof stored electrical energy and a source of generated energy provided bya generator; a powertrain, the powertrain operable to receive as aninput energy from the source of energy and in response to operate one ormore electrically powered motors; one or more propulsors, wherein eachpropulsor is coupled to at least one of the one or more electricallypowered motors; an electronic processor programmed with a first set ofinstructions, which when executed provide one or more functions orprocesses for managing the operation of the aircraft, wherein thesefunctions or processes include a function or process for determining astatus of the amount of stored electrical energy and generator fuelpresently available to the aircraft; determining an amount of storedelectrical energy and generator fuel required to enable the aircraft toreach its intended destination; determining an amount of energy thatcould be generated by the source of generated energy presently availableto the aircraft; determining how to optimally draw energy from thesources of stored electrical energy and generated energy; and in eventof failure or abnormal operation of a component of the powertrain,determining a reconfiguration of the powertrain and a revised controlstrategy for continued flight; an electronic processor programmed with asecond set of instructions, which when executed provide one or morefunctions or processes for planning a flight for the aircraft, whereinthese functions or processes include a function or process for accessingdata regarding the total amount of stored electrical energy andgenerator fuel presently available to the aircraft; determining if theamount of stored electrical energy and generator fuel presentlyavailable to the aircraft is sufficient to enable the aircraft to reachits intended destination, wherein this includes consideration of a firstaircraft operating mode wherein stored energy is used exclusively andconsideration of a second aircraft operating mode wherein a combinationof stored electrical energy and generated energy is used; if the amountof stored electrical energy and generator fuel presently available tothe aircraft is sufficient to enable the aircraft to reach its intendeddestination, then planning a route to the intended destination; if theamount of stored electrical energy and generator fuel presentlyavailable to the aircraft is sufficient to enable the aircraft to reachits intended destination, then planning how to optimally draw energyfrom the sources of stored electrical energy and generated energy overthe planned route to the intended destination; if the amount of storedelectrical energy and generator fuel presently available to the aircraftis insufficient to enable the aircraft to reach its intendeddestination, then planning a route to an intermediate destination,wherein planning a route to an intermediate destination further includesdetermining one or more possible energy and/or fuel providers;determining if available stored electrical energy and generator fuel aresufficient to reach at least one of the providers; generating a route tothe at least one provider; and planning how to optimally draw energyover the route; and a communications element or elements operable toenable data from the aircraft to be transferred to a remote dataprocessing platform or operator and to receive data from the remote dataprocessing platform or operator for exchanging data regarding one ormore of route planning or recharge and refuel sources.
 2. The aircraftof claim 1, wherein the one or more propulsors are a fan located withina duct or shroud.
 3. The aircraft of claim 1, wherein the source ofgenerated energy is a generator that operates to convert a source offuel into energy.
 4. The aircraft of claim 2, wherein the aircraftfurther includes components and processes to enable the one or morepropulsors to be configured for usage in a short takeoff and landingmode.
 5. The aircraft of claim 1, wherein the remote data processingplatform is associated with a recharge and/or refueling platform for theaircraft.
 6. The aircraft of claim 5, wherein the recharge and/orrefueling platform for the aircraft further comprises: a databasestoring information regarding providers of recharge and/or refuelingservices; and a recharge and/or refueling services scheduler.
 7. Theaircraft of claim 1, further comprising elements operable to rechargethe source of stored electrical energy during a braking process.
 8. Theaircraft of claim 1, wherein the powertrain comprises a multiplicity ofcomponents and circuits to enable reconfiguration of the powertrain forsafe and cost effective response to failure or abnormal operation. 9.The aircraft of claim 1, wherein the parameters of one or moreoperational aspects of the powertrain correlate with power output, andfurther, wherein the correlation is weaker than for a powertrain using asource of energy based on combustion of fuel.
 10. An air transportsystem, comprising: a plurality of hybrid-electric powered aircraft,wherein each of the aircraft further comprises a source of energy, thesource of energy including a source of stored electrical energy and asource of generated energy; a powertrain, the powertrain operable toreceive as an input energy from the source of energy and in response tooperate one or more electrically powered motors; one or more propulsors,wherein each propulsor is coupled to at least one of the one or moreelectrically powered motors; an electronic processor programmed with afirst set of instructions, which when executed provide one or morefunctions or processes for managing the operation of the aircraft,wherein these functions or processes include a function or process fordetermining a status of the amount of stored electrical energy andgenerator fuel presently available to the aircraft; determining anamount of stored electrical energy and generator fuel required to enablethe aircraft to reach its intended destination; determining an amount ofenergy that could be generated by the source of generated electricalenergy presently available to the aircraft; determining how to optimallydraw energy from the sources of stored electrical energy and generatedenergy; and in event of failure or abnormal operation of a component ofthe powertrain, determining a reconfiguration of the powertrain and arevised control strategy for continued flight; an electronic processorprogrammed with a second set of instructions, which when executedprovide one or more functions or processes for planning a flight for theaircraft, wherein these functions or processes include a function orprocess for accessing data regarding the total amount of storedelectrical energy and generator fuel presently available to theaircraft; determining if the amount of stored electrical energy andgenerator fuel presently available to the aircraft is sufficient toenable the aircraft to reach its intended destination, wherein thisincludes consideration of a first aircraft operating mode wherein storedenergy is used exclusively and consideration of a second aircraftoperating mode wherein a combination of stored electrical energy andgenerated energy is used; if the amount of stored electrical energy andgenerator fuel presently available to the aircraft is sufficient toenable the aircraft to reach its intended destination, then planning aroute to the intended destination; if the amount of stored electricalenergy and generator fuel presently available to the aircraft issufficient to enable the aircraft to reach its intended destination,then planning how to optimally draw energy from the sources of storedelectrical energy and generated energy over the planned route to theintended destination; and if the amount of stored electrical energy andgenerator fuel presently available to the aircraft is insufficient toenable the aircraft to reach its intended destination, then planning aroute to an intermediate destination, wherein planning a route to anintermediate destination further includes determining one or morepossible energy and/or fuel providers; determining if available storedenergy and generator fuel are sufficient to reach at least one of theproviders; generating a route to the at least one provider; and planninghow to optimally draw energy over the route; and a communicationselement or elements operable to enable data from the aircraft to betransferred to a remote data processing platform or operator and toreceive data from the remote data processing platform or operator forexchanging data regarding one or more of route planning or recharge andrefuel sources; a plurality of aircraft take-off or landing sites,wherein each take-off or landing site includes a recharge and refuelplatform operable to provide recharging services for a source of storedelectrical energy and fuel for a source of generated energy; and a dataprocessing system or platform, wherein the data processing system orplatform is operable to provide route planning data to one or more ofthe plurality of hybrid powered aircraft.
 11. The air transport systemof claim 10, wherein the one or more propulsors of the hybrid poweredaircraft are a fan located within a duct or shroud.
 12. The airtransport system of claim 10, wherein the source of generated energy isa generator that operates to convert a source of fuel into electricalenergy.
 13. The air transport system of claim 10, wherein one or more ofthe plurality of hybrid powered aircraft further include components andprocesses to enable the one or more propulsors to be configured forusage in a short takeoff and landing mode.
 14. The air transport systemof claim 10, wherein at least one of the recharge and/or refuelingplatforms further comprise: a database storing information regardingproviders of recharge and/or refueling services; and a recharge and/orrefueling services scheduler.
 15. The air transport system of claim 10,wherein one or more of the aircraft further comprise elements operableto recharge the source of stored electrical energy during a brakingprocess.
 16. The air transport system of claim 10, wherein theparameters of one or more operational aspects of the powertrain of oneor more of the plurality of hybrid powered aircraft correlate with poweroutput, and further, wherein the correlation is weaker than for apowertrain using a source of energy based on combustion of fuel.
 17. Anon-transitory computer readable medium on which are contained a set ofinstructions, wherein when executed by a programmed electronicprocessing element, the set of instructions cause an apparatuscontaining the electronic processing element to: determine a status ofthe amount of stored electrical energy and generator fuel presentlyavailable to a hybrid-electric powered aircraft; determine an amount ofstored electrical energy and generator fuel required to enable thehybrid-electric powered aircraft to reach its intended destination; anddetermine an amount of energy that could be generated by a source ofgenerated energy presently available to the hybrid-electric poweredaircraft; determine how to optimally draw energy from the sources ofstored electrical energy and generated energy; and in event of failureor abnormal operation of a component of the powertrain, determining areconfiguration of the powertrain and a revised control strategy forcontinued flight.
 18. The non-transitory computer readable medium ofclaim 17, wherein the set of instructions further include instructionsthat cause the apparatus containing the electronic processing elementto: access data regarding the total amount of electrical energy andgenerator fuel presently available to a hybrid-electric poweredaircraft; determine if the amount of stored electrical energy andgenerator fuel presently available to the hybrid-electric poweredaircraft is sufficient to enable the aircraft to reach its intendeddestination, wherein this includes consideration of a first aircraftoperating mode wherein stored energy is used exclusively andconsideration of a second aircraft operating mode wherein a combinationof stored electrical energy and generated energy is used; if the amountof stored electrical energy and generator fuel presently available tothe hybrid-electric powered aircraft is sufficient to enable theaircraft to reach its intended destination, then planning a route to theintended destination; if the amount of stored electrical energy andgenerator fuel presently available to the aircraft is sufficient toenable the aircraft to reach its intended destination, then planning howto optimally draw energy from the sources of stored electrical energyand generated energy over the planned route to the intended destination;and if the amount of stored electrical energy and generator fuelpresently available to the hybrid-electric powered aircraft isinsufficient to enable the aircraft to reach its intended destination,then planning a route to an intermediate destination, wherein planning aroute to an intermediate destination further includes determining one ormore possible energy and/or fuel providers; determining if availablestored energy and generator fuel are sufficient to reach at least one ofthe providers; generating a route to the at least one provider; andplanning how to optimally draw energy over the route.
 19. Thenon-transitory computer readable medium of claim 18, wherein the set ofinstructions further include instructions that cause the apparatuscontaining the electronic processing element to plan the route to anintermediate destination by consideration of one or more of the pilot,aircraft owner, or aircraft operator having an account with a specificrecharge and/or refuel services provider; the recharging servicesavailable at a specific recharge and/or refuel services provider andprices of these services; and the refuel services available at aspecific recharge and/or refuel services provider.
 20. The aircraft ofclaim 1, wherein the powertrain is operable to support one or more of asource of stored electric energy and a source of generated energy, whereeach may be of varying power output, provided that the power output ofthe powertrain is sufficient for flight.
 21. The aircraft of claim 1,further comprising elements to enable depletion of the source of storedenergy by maintaining a safety reserve as fuel for the source ofgenerated energy.